Plz do not comment on this thread.
This thread is just for posting my chapters of C programing in http://forum.xda-developers.com/showthread.php?p=32778306 this thread.
if you wanna comment or ask doubt comment here : http://forum.xda-developers.com/showthread.php?p=32756564
Chapter 1
Lets Talk about programs:
So all of us have heard about the words like programming, programs , code , decode, etc etc ..
but we don't know the meaning of it.. so here it goes..
♣What is a program and programming?
-> For computer to work , we need to give some instructions. This instruction is know as CODE. Where in Each line of code instructs the computer to do something. Set of lines of these codes is commonly known as an program. (this was in common words)
As the definition of program says:
->A computer is designed to accept input, process it and generate output. A set of instructions to perform a task is known as a program. Simmilarly, A set of programs together form an Application.
-> Coding The codes above is known as Programming.
Ohk . Cool . Now lets start learning About flowcharts
♣What is FlowChart? Why use it?
->Flow chart is a graphical representation of a program. It is useful when you are working in a team. Lets say you and me are building a project in C language n you want to show me what u are thinking about the program. you would write in C n compile the program and would show me . But i may not understand how the program worked , in other words i may not understand THE FLOW OF THE PROGRAM you made. So for that reason you make a flow chart of your program on a piece of paper, and then i would understand what you made.
AND flowchart is just like a representation of your program, it is nothing to do with programing.. you cannot put the flowchart in some file in pc n compile n run it . its not possible ..
-> Flow charts are help full in developing complex programs . You will realize it as we go further with the tutorial . I bet you will make a flow chart when you are thinking of a program but you wouldnt know how to put that into set of codes. That is when you would need flow charts.
Chapter 2
FlowCharts
Theory
As Flow Chart is a graphical representation of programs, we need symbols which will help us to graphically represent it. so here they are:
{
"lightbox_close": "Close",
"lightbox_next": "Next",
"lightbox_previous": "Previous",
"lightbox_error": "The requested content cannot be loaded. Please try again later.",
"lightbox_start_slideshow": "Start slideshow",
"lightbox_stop_slideshow": "Stop slideshow",
"lightbox_full_screen": "Full screen",
"lightbox_thumbnails": "Thumbnails",
"lightbox_download": "Download",
"lightbox_share": "Share",
"lightbox_zoom": "Zoom",
"lightbox_new_window": "New window",
"lightbox_toggle_sidebar": "Toggle sidebar"
}
Input:
The Input symbol is used when the user has to input something , in other words it denotes that user will input at this point of program.
eg: the program is about multiplying the two numbers, so the program will ask the user to input two numbers to multiply in this box, 2 and 4
Processing:
The Processing symbol is used to show that there will be some processing in the program now.
eg: after the two numbers are accepted, the process of multiplication is shown in this box. 2 * 4
Output:
The result after processing is done, ie after the two numbers are multiplied , the output is given to the user by this symbol.
eg: 2 * 4 = 8
Decision:
Some times , its essential for the program to make decisions, this can be achieved with the use of this symbol
eg: If you want the user to input two numbers two multiply, but both the numbers should be less then 5, here u can check if the user has given input as per that , if yes then the program will execute(do the work) the way u code for yes, if no then you have to code a different set of code or re run the program.
Subroutine:
This is usefull when you have a big program , you can make different flow charts and then add them together.
Flow Lines:
These are the Lines That will decide where your program will go .
Terminator::
It is like a start for each flowchart, and also the end of flowchart. Also known as Entry point of flow chart and Exit point of flochart.
On page connector:
When your program has the decision boxes, and different conditions satisfy in a different way and end up in a place is where you would use On page connector.
Off page connector:
When your program exceeds the page, and you continue it on some other page then we use Off page connector.
Annotation:
It is a type of comments, which you write for other developers if the part/logic of the part of your program is hard.
================================================== ================================================== ================================================== ==================================================
PracticalLets take an example, that a friend of your asks u to make a program on how to make a tea.
n u say ya ok bro, i will make a flow chart n will send it to you.
so here is the flow chart that you would make
So heres the first flow chart .
lets discuss it in detail (remember the red numbers are just so that you know what i am talking about, u need not write it while drawing flowcharts).
1. It is the terminator. It denotes that your program has started
2. It is the annotation, it is just for the reference of the reader. it is as good as an comment.
3. It is an input box, asks the user to input water, sugar , tea leaves and milk
4. It is an processing box, in this box processes takes place, in this case it is boiling the milk.
5. It is an output box, it tells that the tea is prepared.
6. It is an terminator. It denotes that your program has ended.
================================================== ==================================================*
Lets Take another example:
Suppose i ask you to make a flow chart of how do users register them self at Xda-developers.com.
How would u make it?
Something like this:
So , as you can see,
The terminal is starting the program, then the user inputs his details that are neccesary for signing up(in input box). then those details are stored in the xda developers database(in processing box) , and then the output box shows that you are registered sucessfully..
================================================== ==================================================*
So after seeing two flowcharts i guess you got a better understanding of what flowchart is all about..
So the flowcharts start with a start terminal. and ends with stop terminal. And then there are input boxes for taking inputs and processing boxes for processing the input and there is an output box for output.
So far we learned how to use:
1) Terminator
2) Input Box
3) Processing Box
4) Output Box..
Lets Give you guys an Exercise... At the end of this Post i will put it up.
Now before we move on to use the Decision Box i would like to Show you one more simple flow chart (and if you dont understand it , then i guess i am going too fast in my teaching.. lemme know if you dont get it , pm me or mail me )[/I]
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Decision Box
So while in a program sometimes you have to make decisions.
Decisions like if the user input is right or wrong, username is less than 16 character, password is atleast 6 character etc etc.
This is when you use Decision Box in flow chart.
It is used as follows
When the user is signing up in xda-forum . this is the decision box used after the password is accepted.
It checks , "Is the password greater than 6 characters?, if yes then run so and so codes, if no then run so and so codes" The flow line of Yes have different set of codes. The flow line of No have different set of codes.
For eg:
as you can see , in the decision box, if the Username is greater than 16 characters it shows an error and then runs the program again from where the flow line indicates. If the user name is not greadter than 16 characters then it runs the program normally
Exercise::
Draw FlowCharts For the following programs:
1) To Add two numbers.
2) To multiply the numbers
3) Add two numbers which are single digit only and show appropriate error if user inputs a two digit number
(Hint: Use the decision box to check "is number1 < 10" as if the number will be less than 10 then it will be a single digit number , (we exclude the posibility of negative numbers for sake of simplicity , though will teach you to tackle it in the next chapter))4) Add the two numbers and subtract the addition with their product (eg if the user inputs 2 and 3 , then in processing box write (2*3)-(2+3) )
This Fourth one is important , plz do not skip it as we will discuss on it in next chapter.
Do it on a paper or in book.
mail me at [email protected] your scaned copy or a photo of your flowchart if you want to .. i will see each of them
Or Check From The answers Below.
Answers:
1) Answer
2) Answer
3) Answer
4) Answer
Chapter 3
FlowCharts(...Continued)I hope you have done the exercises and have checked the answers and rectified yourself if you were wrong.
Still i would like to discuss the 4th Problem of the Exercise as i Had some purpose for giving that sum.
So when you were doing the flow chart , you would have encountered a problem.
Lets not go to flow chart directly, lets talk on it as if it were a math problem .
Add the two numbers and subtract the addition with their product: (considering the two numbers are 2 and 3)
Code:
Let the two numbers be a and b.
a=2
b=3
a + b = 5
a x b = 6
(a x b) - (a + b) = 1
NOTE:
You know there are variables in maths?? like x = 2 or x= 7 or y = 10 etc etc..
Ever thought why they are called variables??
It is because their values keep on changing in other words "The value of x VARIATE"
Just Keep it in mind, i would ask you to recollect it after done with this 4th Flowchart Problem
Doesnt it seem too long and boring to write(m talking about (a x b) - (a + b) )?
That's where the flowcharts and all the computer programming languages have a plus point . You will realize it in a minute..
See the flow chart:
See the names underlined with red ink. Sum , Product and Answer.
(referring the flowchart with the above mathematical representation)
Here, when a+b is calculated , the answer is stored in "Sum"
ie:
Code:
Sum= a + b
Similarly, when a x b is calculated , the answer is stored in "Product"
ie:
Code:
Product = a x b
When Product(ie a x b) is subtracted to Sum(ie a+b) it is stored in "Answer"
ie:
Code:
Answer = Product - Sum
Recollect the note above, about the variables and read bellow.
What is a Variable?
-> Variable is a vessel that holds a Value . Where as this value is known as constant.
Eg: x , y , z , a , b , c etc etc
What is Constant?
-> Constant is that value that is stored in a Variable.
Eg, 1 , 2 , 3 , 4 , 5 , 6 etc etc
In all the flow chart above,
These were the variables you used:
Number 1
Number 2
Sum
Product
Answer
You can use the Variable Number 1 again and the value of Number 1 in a different flow chart would be different . Hence it is a variable.
But in any flow chart the value of "1" will remain "1" only.. it wont ever be like 1 = 2.
Hope you are getting my point.
This variable is not just for Flow Chart. Learn Any programing , the knowledge of what is variable and constants is necessary , its like the most basic thing .
So to Sum up and give a summary of variables and constants,
A variable is something like a vessel , a vessel that holds the constants. Constants are the values that are stored in vessel which is nothing but a Variable.
We will talk on this later again when we start the c programming.
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
As in maths , Constants are limited to numbers. For eg , X = 10 , Y = 15 etc etc
But this is not the case with flowchart , In flowchart you can even write a word or a sentence in a variable.
Eg,
Day = " Wednesday"
Month = " October"
Name = " Mihir"
Birthdate = "1st January 0000"
Mobile no = " 123456789"
Pi = "3.148"
Etc etc...
So as you can widely distinguish , variables in FlowCharts are of 2 Types,
1) Character Variable, Eg, Name = "XDA"
2) Numeric Variable(also known as Integer variables , as Integer contains all the numbers ) , Eg, Num = " 12345"
So when you make flow chart you have to Define all the variables you use if they are number? or they are Character?
See the flow chart below to understand how.
As you can see everything is new in this flowchart.
This is the way we represent a program in a better way in flowchart.
Let me explain to you all of its components.
All of which is written in green above, is like a system command sort of a thing.
And all the red color text are variables.
And all of the blue color things are Operators ( mean + , - , x , = etc, we will talk all about operators in next chapter)
System:
START starts the program
NUMERIC defines that the following variables are Integers/numbers and is written always in processing box. (this process is called DECLARATION we will talk about it in a while).
ACCEPT Accepts constants from the user and stores it in the Variable, always written in input box.
DISPLAY Displays the constants stored in the variable.
STOP Stop/terminates the flowchart/program
Meaning of Declaration!
=> When you want to use a variable, lets suppose u want a variable Num1 , Then you first have to tell the computer that:
"Hey bro, i am using a variable named Num1 in my program which is a numeric variable"
which in flowchart is written as :
Code:
[COLOR="SeaGreen"][B]NUMERIC[/B][/COLOR] [B][COLOR="Red"]nNum1[/COLOR][/B]
As you can see that we are talking to the computer and telling that we are using the variable of this name , it is AS good AS a process?
Hence, it is written in a Processing Box.
As you can see i am prefixing all the numeric variables with n , and you might be wondering , what is this crazy guy talking ?
Basically,
All the variables are prefixed to show what type of variable it is when we use them .
meaning, when we use a numeric variable , we prefix it with n, when we use a character variable we prefix it with c
You can name the variable what ever you like , a, b ,c sum , interest , principle,Name, blah blah etc etc.. anything you like cuz when you will write it in flow chart it will be like nSum, nInterest, nPrinciple , cName. So u will know that Sum ,interest & Principle are numeric variables and Name is a Character variable. Hope now you understand whats the use of prefixing n and c in variable name.
Lets talk about the above flow chart step wise now(referring the numbers in the image above):
After the program starts,
1. There is a Process box. As you know it declares (recollect, declaration means to tell computer that you are using this variable) the variable, hence it is in the process box. In this box the Variables are declared as Numeric and hence are prefixed with n .
2. There is a Input box. What do we do in input box? we take input , and hence there is a proper word defined for it . Accept , and we then write all the variables that we want the values of , from the user.
3. There is a processing box, It adds the two numbers and then stores the value in the Variable Sum which is numeric ( nSum) (it will be clear when i teach you operators in next chapter)
4. There is a Output box, its purpose is to DISPLAY , hence we write Display and then we write all the variables in the Output box that we want to display.
and the program terminates..
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Dont give up, let the things sink in. It will take time , you will learn! Trust your self
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I would like to advice you to read this again. As you will get a better understanding of it now. And i have added some things in it so dont skip it.
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Input:
The Input symbol is used when the user has to input something , in other words it denotes that user will input at this point of program.
eg: the program is about multiplying the two numbers, so the program will ask the user to input two numbers to multiply in this box, 2 and 4
When you want to accept the values from user , you write it in an Input Box. lets suppose you want to Add two numbers , for that you need Three Variables, One variable for storing The first number, second variable for storing the second number , third variable for storing the value of the addition of two variables. And lets name these variables now, nNum1,nNum2 and nSum. So how will you write it in input box?
This way
"Accept nNum1 and nNum2"
Processing:
The Processing symbol is used to show that there will be some processing in the program now.
eg: after the two numbers are accepted, the process of multiplication is shown in this box. 2 * 4
Two things that can be in processes :
The first process box is above, it is used to declare variable with its type,
lets consider the same above example , then u wud write it
"Numeric nNum1, nNum2 and nNum3"
And then you need to add those numbers? correct so you would add it in another processing box like this:
"nSum = nNum1 + nNum2 "
Output:
The result after processing is done, ie after the two numbers are multiplied , the output is given to the user by this symbol.
eg: 2 * 4 = 8
The main purpose of Output box is to show the output.
See the pic below
As we want to display , so we write "Display" in this box. Suppose you want to display Sum calculated above, you would do it this way:
"Display nSum".
We can also write what ever we want in double inverted comas.
Eg
Code:
Display "Hie this is Mihir"
You can even append a variable after it, the constant stored in that variable will be displayed,
Lets suppose there is a variable nNum , in which the Mobile number of a user is saved and the number is 123456789, then you can display it this way:
Code:
Display "Your Mobile number is" nNum
This will display , Your Mobile number is 123456789
Decision:
Some times , its essential for the program to make decisions, this can be achieved with the use of this symbol
eg: If you want the user to input two numbers two multiply, but both the numbers should be less then 5, here u can check if the user has given input as per that , if yes then the program will execute(do the work) the way u code for yes, if no then you have to code a different set of code or re run the program.
Here checking statement means to check something. Eg nSum < 10 or nSum > 10 , nNum <100 etc etc (as of now it consists only of Single Check statement , like you can just see if its a variable is less that 100 and similar things . You cant compare it with two things like a variable is greater than 50 but is less than 100. As of now i cant. We first have to understand operators, after done with operators , we will come back here and talk about it.)
If you were to check if the nSum is less than 100 you would write:
"Is nSum<100 ?"
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Plz read the output box again i have added something. This is for the users who have read the post yest. And i have edited it just now.
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A flow chart for registration.
i guess you can now understand this flowchart above , and i need not explain it to you.
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Chapter 4
Operators
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Hope the above image , clears your mind about what is variable and constants.. If you still have any confusion about variables and constants then mail me at helpline mail : [email protected] or PM me..
I devote this chapter to Operators..
Operators: The symbols used to make the computer do an operation is know as an operator .
There are various various types of operators:
1)Arithmetical Operators
2)Conditional Operators
3)Relational Operators
1)Arithmetical Operators :
-> Operators used for doing mathematical operations is know as arithmetical operators. This includes the following :
=
+
-
*
/
%
you may be familiar with all the mathematical expressions above, rather than this, one %.
This is not a percentage , its a modulor division operator. Its name is Modulus.
The division operator yields the Quotient as an answer, where as Modulus yields the Remainder as an Answer.
as you can see above,
when you write an expression as 13/2 it will yield an ans 6 . Therefore, 13/2 is 6 or may be 6.5 (calculation in flowchart is not so precise as it is just to understand the flow of the program and not for calculations)
when you write an expression as 13%2 it will yield an ans 1. Therefore, 13%2 is 1.
====================
2)Conditional Operators
Operators that define conditions are known as conditional operators.
They include these
|
&
This | is "OR" operator. It is used when you want to define any conditions like : a<10|a>15. This means either a is less than 10 OR it is greater than 15 , then its yes . (refering to the decision box, cuz thats the only place where you want to put up conditions right?) Only one of the two conditions must be satisfied , in order to make it a YES
If not even one condition is satisfied then it is a NO , n it will run different set of codes .
Image below will help you understand it.
==============================
The second operator is & "AND" operator. This is used when you want conditions like : a>100&a<200. in this , a should be greater than 100 AND a should also be less than 200 , if both the conditions satisfy then only it is a yes, if either of the condition is not satisfied, then its a no.
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3)Relational operators:
->Operators used for relating two variables are known as Relational Operators
They are as follows:
==
<
>
<=
>=
!=
Note: '=' is used to assign the value, eg , a=4, this means a is equal to 4, where as , a==4 , is a relational operator, it checks , IS a is equal to 4?
The two operators == and != are new to you, i explained the first one above,
the second one != is "not equal to", it is used to check , eg , Is a!=4?,if a is not equal to 4 thn its a yes, if a is equal to 4 then its a no.
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A flow chart to check whether the number input by the user is positive or negative?
Try this on your own , n then see the answer below,
You would notice , there is a circle after the processing box..
It is an on page conector. When more than one flow lines are conected to something , then this is used, (i havent used it in any of the above eg of flowcharts, just to teach you bit by bit.)
This is what i used before:
this is what is to be used :
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This was it Small Chapter 4. On operators..
If you have done this much ,then be proud of your self, cuz u have learned half of the basics of C programming
Next chapter it about Subroutine and off page conector. And then we will commence out voyage in C programming
Chapter 5
Subroutines And Off-Page-Connector
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So as you have seen many flow charts above, u have came to an end of learning the flow chart, are are soon going to learn about C programming.
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So lets talk about Subroutine:
What is Subroutine?
-> It is a symbol used in Flow charts to represent the programs clearly.
You will understand it after you see the flow chart bellow.
Lets suppose you were to make a program to add the numbers (we did it before in Chapter 3) , but using subroutine makes it tidy graphical Representation , and also it is easy to understand while reading it. :
As you can see above , the function of adding the two numbers is separated from the flowchart for better representation , this is known as an Modular Approach of Programming.
(not talking just about FlowCharts , i Am talking of C programming language .)
Modular Approach of programming is , to keep the main code in a file , and then the operating codes in a separate file , as you can see above, the main code is separated from the code that adds the numbers.
It is not of a great help when such a small flowchart, but when u have a full calculator in which you would add , subtract , multiply , divide etc etc , this approach would be the best . :good:
NOTE:at the end of the subroutine , we use a terminator with "RETURN" , and not "STOP"
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Lets take another Example.:
You wanted to make a flowchart of a program , a program that adds and subtracts both .
Then it would be represented this way :
(all the three images is one FlowChart Only)
Each image above is like a different page in a book.
So if your flow chart ever exceeds the page in a book or page in any document, then you use the off page Connector.
Lets first talk about subroutine.
As u can see above, the Subroutines add and subtract are separated from the flowchart , you can write it on any page as long as those pages are kept together .
When the page comes to an end, we use a Off-Page-Connector, and then name it what ever we like, and in a new page we make a new Off-Page-Connector with the same name, as you can see a connector with name "A" is on the both page, so the connector "A" on the first page , conects with the conector "A" on the second page , Same way with the connectors named "B"
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One more eg and we are done With Flowcharts
A flowchart , to show a program .
The program takes the marks of the students who gave an entrance exam for College, Subjects are Math,English and French. If in each subject a student scores atleast 35 marks and the average of the 3 subject is atleast 50 marks , Then a selection letter from the college is sent , if not , then a rejection letter is sent. Also count the number of selection letters and rejection letters sent.
Note:I wont explain this flow chart. If you can understand it on your own then you are good to go further with C programming , if you cant then please read the chapters again and try understanding it again and then proceed with programming.
The only new thing in this is :
nSelect = nSelect + 1
Lets suppose nSelect is a variable with a value 0 in it , then you can say
nSelect = nSelect + 1 which means , nSelect = 0 + 1
And then suppose nSelect is 1 then
nSelect = nSelect + 1 means nSelect = 1+1 which comes to two.
You can use such type of statements in programing .
Remember ,
The Right Hand Side of an equation is calculated and then stored in the variable Left Hand Side,
NSelect + 1 is calculated and the ans is stored in nSelect on the Left Hand Side. It works as an counter.
And yeah!! you are done with flowcharts.. We will start with Programming ASAP ..
C Programming Begins!!!
So today we would have started with C programming ,but according to me and my fellow developer friend with whom i discussed of how to teach it to you and decided that we will teach you some extra things. As we are secondarily studying this for learning Android stuff though not only for android , we will try to teach everything about C but we will also try to teach you some extra things that will be helpful while you start with your android development .
So the main things are :
What is Computer?
What is an Operating System?
Where is C usefull in all this?
What is android?
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What is computer?
-> The definition of computer have changed as it has got many changes in it. Years before when computer wasnt invented , the person who used to do calculations was referred as a Computer as he used compute the Mathematical problems. But as the machine was invented to do the calculation , The machine was then named as "Computer".
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What is a Operating System?
=> Years Ago when computer was first invented,
it had a monitor of small size, one full room of chips and stuff (today it fits into a small box and we call it CPU) the name of the room was Central Processing Unit , (the room was the core of the computer , and as you know a room is also called as a Unit) . That room used to get commands from other room where the input from user was taken , and then processed and sent back to the same room for displaying it on Monitor. Hence it was a processing room too. So the room with chips used to Process things , it was the Core thing and hence it is named as Central Processing Unit(CPU).
(If you are interested in all the things I said above, then you must study Computer Architecture , as study of all these stuff is known as Computer Architecture .)
When this Computer was invented , it was just for the sake of calculation , you can say it was a 2 room huge calculator. And when you start the computer , You just see a black screen , and then you had to write the whole calculator program in a programming language you like (idk what language was used at that time ) and then do the work. The calculator program was very huge and it was very tiring job of writing it everytime you turn on the computer. So then someone invented "something" that stored the things in it. This "something" was named as Memory. As it stored the calculator program, it was kind of a Memory for the Brain(CPU) of the computer, Hence named as Memory. (This memory was very small it wasnt even 1kb ) And then the Calculator Program was written again and then stored to the memory . So everytime you turn on the Computer you dont have to Write the whole calculator program you just have to write some set of codes to go to memory and run that calculator program. Eventually when the need of computers increased from just calculation to many other Office work , like Storing the customer information, making the list of expenses and profits of an company many such applications were made . But still to run any of these application , some set of codes were neccesary and hence it was useless till some extent for normal people. So a new era was started, The era of operating systems. It was like you will have applications for using APPLICATIONS, eg if you want to use calculator in windows operating system, you will go to Start menu and then accesories and then select calculator. This is called GUI, meaning Graphical User Interface. Today we can make a folder by right clicking and selecting "New Folder" this wasnt the scenerio at that point of time , they had some set of commands to create a folder.(even today you can make a folder with this command in Command Prompt "mkdir NewFolder" mkdir meaning make directory , and then "NewFolder" is the name of the folder. If we want to see what folders we have in c drive, we just go to MyComputer and then go to c drive, this wasnt the case at that time, they had to write set of commands to navigate till that directory , and then had another command to List all the files and folders in that place. So everything was based on Commands Given by the User. So an need of Operating System was essential , where in commands were given by user interface(eg right clicking and making a folder is as good as opening command prompt, navigating to the location and then giving commands to make a new folder .) So when all these things are put together and then the need of Commands is decrease for day to day work , this package of software is known as Operating System.
There are different companies making Operating Systems depending upon the hardware capabilities of a Computer. eg, Windows, Linux and Mac(apple).
Note: The Definition of an Operating System is way too big than i explained above, but this is what you should know as of now.
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Where is C usefull in all this?
=> The whole operating System is made in C language. It is a fact that, Windows consists of 13,000 lines of codes where in only 800 lines are not writen in C launguage . Now you can see what is the value of C . (will be writing C rather than C language ) C is widely used in making Operating Systems , Games and Kernels in other electronic Devices.
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What is kernel?
=> A set of codes writen in C language that lets the Software and the Hardware communicate is known as kernel. For eg , if you press the volume Down button (hardware) how does android phone knows that the volume down button was pressed and the he has to lower the volume by a level in the phone?
See the image below:
The Hardware says the kernel that the user wants to lower the volume , the kernel comunicates with Operating System(OS) and tells to lower the volume by one level , and then it displays that the volume is decreased .
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Why C in everything?
=> C is widely used in everything because it is very fast as it is in direct contact with Hardware via kernels. So it is faster than any other programming language. It is not only used in computers. The Food Processor with Timing, the Tv Remote etc everything has C in it.
===================================================
What is Android?
=> Android can be simpt explained by saying "The mobile version of Linux is known as Android"
This was just a chapter for some extra information that would be usefull in your future when you will start doing some work in android or windows, or even when you will try to make some programs in C while you are learning from this tutorial.
Chapter 1 Theory On C prgramming
So basically What is C?
=> C is a programming language developed at AT & T's Bell Laboratories of USA in 1972. It was designed and written by only one person "Dennis Ritchie". In the late seventies C began to replace the other programming languages like PL/I,ALGOL,etc. No one pushed C neither was it 'official' Bell Labs language nor was it advertised by any means. Still C's reputation spread and its pool of users grew. Ritchie seems to have been rather surprised that so many programmers preferred C over the older languages, including FORTRAN. Still it is choosen over the newer languages like PASCAL and APL.
Probbaly , why C seems so popular is because it is reliable, simple and easy to use. Moreover, In an industry where newer languages, tools and technologies emerge and vanish day in and day out, a language that has survived for more than three decades has to be really good.
An opinion that is often heard today is -
"C has already superceded by languages like C++, C# and Java, so why bother to learn C today!!". I seriously beg to differ with this opinion. There are several reasons for this(according to the aurthor of the book "Let Us C"-Yashwant Kanetkar, and i agree with him):
I believer that nobody can learn C++ or Java directly. This is because while learning these languages you have things like Classes , Objects, Inheritance , polymorphism , Templates , etc. and also the elements like loop , if-else, nested if-else, switch,etc. These elements like loop etc should be learned in C , then about objects in C++ and then Exception handling in Java , so it is like a proper flow in the boat of Knowledge. Though this Three-Step learning process may take more time, but at the end of it you will definitely find it worth the trouble.
C++,C# or Java make use of principle called Object Oriented Programming(OOP) to organize the program. This organizing principle has lots of advantages to offer . But eve while using this organizing principle you would still need a good hold over the language elements of C and the basic programming Skill
Though many C++ and Java based tools and frameworks have evoleved over the years the importance of C is still unchanged because knowingly or unknowingly while using these frameworks and tools you would be still required to use the core C language elements -another good reason whu one should learn C before C++ , C# or Java.
Major parts of popular operating system like Windows, UNIX, Linux are still written in C (As we talked on it earlier) This is because even today when it comes to performance (speed of execution Nothing beats c) Moreover, if one is to extend the operating system to work with new devices one needs to write device driver programs. This programs are exclusively written in C (this is what you will do when you will build android kernels after learning C)
Mobile devices like Cellular phones and palmtops have become rage of today. Also, common consumer devices like mirowaveovens , washing machines and digital cameras are getting smarter by the day. This smartness comes from a microprocessor, an operating system and program embedded in this devices. These programs not only have to run fast but also have to work in limited amount of memory. No wonder that such programs are written in C. With these costraints on time and space, C is the language of choice while building such operating system and programs.
You must have seen several professional 3F computer games where the user navigates some object, like say a spaceship and fires bullets at the invaders. The essence of all such games is speed. Needless to say, such games wont become popular if they take a long time to move the spaceship or to fire a bullet . To match the expectations of the player the game has to react fast to the user inputs. This is where C language scores over the other languages. Many popular gaming frameworks have been built using C language
At times one is required to very closely interact with the hardware devices. Since C provides several languages elements that make this interaction feasible without compromising the performance, it is the preferred choice of the programmer.
I hope that these are very convincing reasons why you should adopt C as the first and the very important step in your quest for learning programming languages.
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Getting Started with CCommunicating with a computer involces speaking the language the computer understands , which immediately rules out English as the language of communication with computer. However, there is a close analogy between learning English language and learning C language. The best method to learn English is to first learn the alphabets used in the language , then learn to combine these alphabets to form words, which , in turn, are combined to form sentences and sentences are combined to form paragraphs. Learning C is similar and easier . Instead of straight-away learning how to write programs , we must first know what alphabets, number and special symbols are used in C , then how using them,constants, variables and keywords are constructed and finally, how are these combined to form an instruction. It is illustrated below:
=========================================================================
C Character SetA character denotes any alphabet, digit or special symbol used to represent information. The Valid aplphabets, numbers and special symbols allowed in C are :
We would talk about what are variables,constants and keywords and set up the programming environment and also make our first prorgram with its flowchart
CHAPTER 2
I can bet you will relate most of the things with C programming , from flowcharts.
When you run an application , it first reserves the memory required for it to run . Lets suppose you are playing a game on computer, "pinball", this game will first reserve the memory locations in the RAM or storage. And then only THE PINBALL game can access those memory locations. The image below depicts is properly.
as you can see above , memory is made up of cells, each cell has its address (0x111 to 0x142 are the adresses, dont worry about the numbers like 0x111 n stuff i just wrote it to show you , the real memory locations are like 2031576,2031577,2031578,2031579 and so on. We will see it in real when we go further down with the chapters )
Lets say your computer has a memory from 0x000 to 0x999, and then you open the pinball game , the pinball game needs 32memory cells, and it started getting cells from 0x111 and then reserved till 0x142 so that it can run smoothly , and lets suppose you open another app in backgroud , lets say you opened Calculator, and also suppose Calculator needs 50 cells of memory , then it willl start from 0x143 to 0x193.
These cells are nothing but Bytes.
1Gigabyte = 1000Mega Byte
1MegaByte= 1000 Killobyte
1Kilobyte = 1000 byte
This is what we know right? its wrong
1Gigabyte = 1024 Mega Byte
1MegaByte= 1024 Killobyte
1Kilobyte = 1024 byte
What is 1 byte equal to??
1byte = 8bits
NOTE: Google this "1 byte = how many bits"
You will see this at the start , as you can see it works like a converter, just goof around with it have a lil fun n learn mean while.
This was just off topic things, but keep these things in mind while learning C , this is like the general knowledge required for learning C , so now we are starting with Real C programming.
===================================================================================
So now what is variables?
Various Definitions:
Code:
"A variable is the name for a place in the computer's memory where you store some data."
"A variable is a way of referring to a memory location used in a computer program. "
Lets not go into theory again , lets talk about a program in which you want to add two numbers.
First of all you want to accept 2 numbers from users , add them and then store it to another variable?
Lets say you accept two numbers 'x' and 'y' from the user , you cant just write x + y, right? cuz x + y what? you will have to use one more variable 'z' and then store the value sum of 'x' and 'y' in it. ie z=x+y
so now here the three variable 'x' , 'y' and 'z' are variables, agreed?
so these variables WILL be stored in memory?
Each of them will use their own memory cells? or to be precise each one of the variable will use a BYTE from memory?
lets say the three memory locations used are 0x200,0x201,0x202
So you can conclude that the NICKNAMES of the memory location 0x200,0x201,0x202 , are 'x' , 'y' and 'z' respectively.
which in other words means the variable 'x' is reffering to 0x200 , so what ever you store in variable x is gonna be stored in the memory cell with address 0x200 and the same with 'y' and 'z' . so the above definitions are true, If you may read it again , you will understand better . Still you dont know what is DATA in this right? we will talk about it in a while.
What are constants?
The value of a variable is constant.
lets talk about the above program again , the variable x, y and z.
The user inputs the number 2 and 4,
so x = 2 , y = 4 and as these numbers are supposed to add and the answer is stored in z , so z=6.
now the value of x will change from program to program , if i make another program , i can use variable x and it may have a different value.
But the VALUE of value of variable , (2, is the value of x) this will never change, 2 will remain 2 , it wont ever mean 3, like 2=3 or something.
Hence it is a constant. This constant is stored in memory. The image below depicts is clearly.
============================================================================
Lets get in actoin?
So lets download the compiler now.
So the compiler we gonna use is DJGPP, it it like command line GCC (GNU C Compiler) , we will write program in notepad++, and then save it and then open up command prompt and then compile it from there and then we will get an .exe file .(dont worry if you arent getting it, everything will be taught )
Links:
DJGPP
Notepad++
How to download things?
For DJGPP:
select these fields:
The selection of Operating system may change according to your OS. If on Windows 7/vista select windows XP in that os section.
then click on tell me which files to download .
then download each of the zip file .
NOTE : If you are on linux then you have gcc compilers already, google it how to use it.
For notepad++:
go to the link above , then click on download button on left botom panel:
then:
.
===========================================================
Put the downloaded files from DJGPP in a folder named DJGPP.
now open the note pad plus plus exe and install it ..
then copy the DJGPP folder to C drive:
now open notepad++
and then write the name of the files in that DJGPP folder in the notepad++ (write unzip32 and then the file name):
and then save it as DJGPP.bat (dont forget to write .bat in that DJGPP folder..
if you have done the downlaod the way i have said and you have 8 files in the folder then copy this and paste in notepad :
Code:
unzip32 bnu2211b
unzip32 djdev203
unzip32 faq230b
unzip32 gcc472b
unzip32 mak3791b
unzip32 pakk023b
unzip32 rhid15ab
unzip32 txi412b
now go to DJGPP folder and open this DJGPP.bat file.. it will extract things for you..
now go to start menu , right click on my computer then click on properties:
now follow the instructions in the screen shots below(in some screen shots i have show the PATH in note pad, its jst to show you the path in bigger font. you need not write it on notepad):
click on advanced system properties, for windows xp users, you will have a box opened like the image below , click on advanced tab , for vista users IDK i never used Windows vista goof arround with it you will find what to do..
click on environment variables
click on path and then click on EDIT .
Note that in the path , there should be a ':' semicolon , then write c:/djgpp/bin;%PATH% , then click on ok.
now click on new
write these things in the Variable name and variable value , click on ok , then again ok then again ok. and you will be done..
now we have set up our Compiler .
Now lets write our first C program, just to check whether the compiler is running or not.
copy this and paste it in notepad++ ,
Code:
#include<stdio.h>
void main()
{
printf("Hello XDA!!!");
}
now save it with the name hello.c , dont forget to write ".c" at the end.
now open command prompt ,
write
Code:
cd desktop
then write
Code:
gcc hello.c
then write
Code:
a
if you got something like this then you are done.. if you got a error like Gcc is not an internal comand or something.. you messed it up , try the steps above from setting the environment variables.. and still you fail then you mail me at [email protected]
NOTE: Dont worry , we were just checking if its working or no , m gona teach you to use command prompt soon trust me , the boring part is over now. Its all the fun now :good:
Chapter 5 - Part II
Integer and float conversions
In last tutorial you learnt about the operators used in C programming. Now we will see about how to use them effectively, i am making this tutorial by writing it because it has some tables which will take time for you to understand, and for that its better to write it than to show it in video.
So in order to effectively develop C programs, it will be necessary to understand the rules that are used for the implicit conversion of floating point(means a float variable) and integer values in C. These are mentioned below : (read them carefully , remember float variable, floating point and real variable , all mean one and the same thing)
An arithmetic operation between an integer and integer will always yield an integer result.
Eg. 2*2=4
An operation between real and real will always yield a real result.
Eg, 2.000000 * 2.000000 = 4.000000
Point to remember: : Float variable has 6 digits after the decimal , so if you write ,
Code:
#include<stdio.h>
main()
{
float a;
a=10;
print("%f",a);
}
then it will print 10.000000 as float value has 6 digits of precision..
An operation between an integer and real will always yield a real result.
eg, 6/2.0 = 3.000000 , you see that 6 is integer , 2.0 is real and they are divided, the 6 gets promoted to real value (6.000000) and then 6.000000 is divided with 2.000000 and the answer is 3.000000
Lets list all the operators we know so far:
+ (Addition operator)
- (Subtracting operator)
* (Multiplying operator)
/ (Dividing operator)
% (Modulus)
= (Assignment operator)
== (Equality operator)
Lets suppose you were to write a expresion like this:
Code:
x=2*3+4;
Now there are two possibilities in this ,
The compiler can first multiply:
Code:
2*3
and then add 4 to it.
OR
The compiler can first add:
Code:
3+4
and then multiply it by 2.
These two possibilities can create confusions while making programs, hence to solve these, C has something known as "Operators Precedence".
See the Image Below :
As you can see, that the */% have more precedence then the + -, hence , When there is a expression like:
Code:
x=2*3+4;
First multiplication is carried out , and then it is added. and then it is assigned(the assignment operator has last precedence) to the variable in left.
NOTE: The =! is NOT EQUAL to operator and is used when you compare it. will be explained in following chapters with examples.
===========================================================================================================
In addition to these operators, there are more operators, which we will see as we need them further, and will be explained as we encounter them.,
Chapter 6 (DECISION!! DECISION!! DECISION!!)
Chapter 6
If you have a calculator which will just ADD the two numbers, then calculator will be pretty useless , wont it?
Hence,There is something in the calculator that decides whether to add or subtract or multiply the two or more numbers provided by the users. This is when we need decision control.
The C language too must be able to perform different sets of actions depending on the circumstances. Actually, this is what makes C popular and very widely usable.
C has three decision making instruction(Reminder:a line of code is instruction)
If Statement
If-Else Statement
Switch
The if StatementLike most languages, C uses the keyword(if you forgot what is keywords check out the FAQ) if to implement the decision control instruction. The syntax(look FAQ) of if statement looks like this:
Code:
if(condition)
{
[B][I]code[/I][/B];
}
where the CODE is the instructions that you want to run.
And if the CONDITION is true then the CODE is executed.
The keyword if tells the compiler that what follows the keyword if in the ( ) "parenthesis" is the condition. If this condition is true then the CODE in the pair of { } "braces" is executed. if the condition is not true then the statement is not executed, in fact the program skips it.
How to evaluate if the condition is true or false?
With the help of relational operators.(will be taught in the second part of chapter 5, when it will be updated for now just remember that the operators used for relating is known as relational operators Eg. == , !=, < , > , <= , >=.
== is to compare the right hand side with the left hand side and != means not equal and others are simple. Will be taught in detail in Chapter 5 part 2 i will link you as soon as that chapter is done by my friend.)
Lets try a program now:
Code:
//This is a coment
//A program for demonstration of [B][I]if[/I][/B]
#include<stdio.h>
main()
{
int number;
printf("Please enter a number with less than 100\n");
scanf("%d",&number);
if(number<100)
{
printf("What a good student you are!!");
}
}
NOTE:
Never put semi colon after if statement Like this
Code:
if(a<10);
printf("A is less than 10!");
As the program will think that you terminated the if statement after checking the condition , it will think of it this way
Code:
if(a<10)
{
}
printf("A is less than 10!!");
So no matter what the value of a is , it will always print A is less than 10.
A flowchart for the above program to make things clear:
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Another Eg:
If your bill is above 10$ in McDonald's then you get 5% discount, if not then no discount.
(try making a flowchart your self , and then see the C program below)
Code:
#include<stdio.h>
main()
{
float billamount;
[COLOR="Green"]/*float data type because bill can be in decimal. eg 10.40$*/[/COLOR]
int discount;
[COLOR="Green"]/*discount will remain 10% only*/[/COLOR]
float totalamount;
[COLOR="Green"]/*the amount after deducting the discount from the bill we will store the value in the "totalamount" variable*/[/COLOR]
printf("Enter your bill amount in Dollars\n");
scanf("%f",&billamount);
if(billamount>=10)
{
discount=5; //If billamount will be more than or equal to 10$ then we will give discount of 5%
}
totalamount=[COLOR="RoyalBlue"]billamount[/COLOR]-[COLOR="Red"]billamount*discount/100[/COLOR];
[COLOR="Green"]/*here [COLOR="red"]billamount*discount/100[/COLOR] is to calculate the percentage and then subtract it with the real [COLOR="RoyalBlue"]billamount[/COLOR]*/[/COLOR]
printf("The total amount is : %f",totalamount);
}
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The If Else Statement
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
The if -Else statement is the real thing, the if statement was derived from it. Will explain you how and why at the end of the If-Else discussion .
The Syntax(syntax means general form )of the IF-ELSE statement is.
Code:
if(CONDITION)
{
CODE If true;
}
else
{
CODE if the CONDITION is false;
}
Lets go through it Step by step:
The CONDITION is evaluated
The CODE IF TRUE will run if the CONDITION is TRUE
if the condition is false then the CODE IF THE CONDITION IS FALSE will run.
Lets see a example
Code:
/*A program to add or subtract the numbers*/
#include<stdio.h>
main()
{
int a,b,c; /*a and b for accepting number for user and c for storing the addition or subtraction*/
char op;
printf("Hello, Please enter your operation (Addition or Subtraction only)?\n");
scanf("%d%c%d",&a,&op,&b);
if(op=='+')
{
c=a+b;
}
else
{
c=a-b;
}
printf("The answer is : %d",c);
}
Some examples tested in the program.
Found it complicated? The lets simplify:
scanf("%d%c%d",&a,&op,&b);
The %d will accept the first integer and save it in a
The %c will accept the Operator(+ or - ) and save it in op
The %d will accept the second integer and save it in b
Then the If will check if the op=='+', if it is + then it will add and store the answer in the variable c. It will skip the ELSE .
If op is not + then it will skip the if and the codes in the Else will run, meaning it will skip the codes in the if and then subtract the two integers and then store the value in variable c.
After this the printf functions prints the variable c, which is the answer.
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Revising Stuffs
---------------------------------------------------------------------------------------------------------------------------------------------------------
Let me brush up your basics again:
%d is for integers
%c is for characters
%f is for floats
Defining: To tell the computer you want a variable of int/float/char type is called as defining a variable.
Eg.
char a;
int b;
float c;
Initializing: To give a value to a variable is known as initializing a variable.
Eg.
char a;
a='Z';
int b;
b=2;
float c;
c=3.000000; (decimal is not neccesary while initializing, but when you will print a float variable , you will see the decimals)
CAN ALSO BE INITIALIZED THIS WAY:
char a='Z';
int b=2;
float c=3.000000;
Note: To initialize a char type of variable, you use ' ' single inverted commas, Eg. char a = 'Z';. This is what we have used in the if condition in the above example , if(op=='+');
When we write only the variable name like, (supposing int x = 10
printf("%d",x);
We will get 10 as output , that is the value of the varaible.
But when we write a variable name with ampersand(&), (supposing int x is located at 25834 on the memory)
printf("%d",&x);
We will get 25834 as output, as the &(ampersand) is a operator that tells the program to related the variable's address rather than its value.
Now you know why we write
scanf("%d",&a);
Rather than:
scanf("%d",a);
---------------------------------------------------------------------------------------------------------------------------------------------------------
Switch
---------------------------------------------------------------------------------------------------------------------------------------------------------------When we have to make only two decisions depending upon only TWO possibilities then we use If-Else.
Eg,
If the numbers are even then add them and if not , then subtract them
If the user is male then he have to pay 25.5% as tax from his income and if not male then 25.0% tax from her income
If a number less than 10 then multiply it by 100, if it is not less than 10 then divide it by 100, Etc.
But what if you want to make various decisions depending on various possibilities
Eg,
If the number is less than 10, then add 10. If the number is greater than 20 then subtract 10, if the number is 0 then add 20.
If the character entered by user is 'a' then print A, if 'b' then B,if 'c' then C, if'd' then D, if 'e' then E , Etc.
This is when you use switch case.
The Syntax of switch case is as follows:
Code:
[COLOR="DarkGreen"]Switch[/COLOR](CASE NUMBER)
[COLOR="DarkGreen"]Case [/COLOR]NUMBER 1:
{
CODES HERE;
}
[COLOR="DarkGreen"]Case [/COLOR]NUMBER 2:
{
CODES HERE;
}
[COLOR="DarkGreen"]Case [/COLOR]NUMBER 3:
{
CODES HERE;
}
[COLOR="DarkGreen"]Case [/COLOR]NUMBER 4:
{
CODES HERE;
}
Default:
{
CODES HERE;
}
Post Under Construction
[APP][2.2+]Dynamic Pin- Lock ur screen&apps with state of art authenticating algorith
Lock your screen and mobile applications with state of art authentication technology.
Dynamic pin app helps you to secure your PIN from shoulder surfing .
When you type in the same PIN every time, there is a good chance for your friends , electronic surveillance or others to know the PIN . How will you avoid that ?
Dynamic Pin changes the pin based on the expression you set in the application. After every use, your Pin is destroyed and only the user who knew the expression can evaluate the new Pin from the clue , the matrix . Deducing the expressions from pin is not a trivial task . An example is provided at the end.
Now you can set any expression like a+d , a*f , g-c ...
Basic Pack :
Unlimited application locks.
This pack enables operations among the matrix elements using + , - , * , / , % , ^ .
Examples :
(a*d)+5 - Multiply corner elements of the first row and add 5;
(a+d+m+p) - Add corner elements of the matrix.
Advanced Pack :
This pack enables MIN (a,b), MAX (m,p) functions along with basic pack.
More functions are planned for future releases.
Examples :
MIN(a,d ) - Minimum value between a and d .
MAX(a,b ) - Maximum value between a and b .
FAQ :
1. What is the validation code?
Validation code is a number available on secured lock screen as a toast message. In certain devices message is showed only when emergency dialler is clicked.
2. What is the PIN set before entering one time validation code ?
"1234"
Note - In devices from HTC and Sony matrix will be shown when Emergency Call window is opened on the lock screen.
Example :
Expression set in the application : a+b
Matrix on lock screen :
a1 b3 c4 d7
e2 f8 g2 h9
i5 j4 k1 l0
m1 n4 o6 p2
Now pin is a+b = 1+3 = 0004
Matrix on lock screen :
a2 b5 c1 d9
e7 f1 g2 h8
i2 j0 k5 l2
m8 n1 o7 p3
Now pin is a+b = 2+5 = 0007
mail me your feedback at [email protected]
Basic Pack :
Unlimited application locks.
This pack enables operations among the matrix elements using + , - , * , / , % , ^ .
Examples :
(a*d)+5 - Multiply corner elements of the first row and add 5;
(a+d+m+p) - Add corner elements of the matrix.
Advanced Pack :
This pack enables MIN (a,b), MAX (m,p) functions along with basic pack.
More functions are planned for future releases.
Examples :
MIN(a,d ) - Minimum value between a and d .
MAX(a,b ) - Maximum value between a and b .
FAQ :
1. What is the validation code?
Validation code is a number available on secured lock screen as a toast message. In certain devices message is showed only when emergency dialler is clicked.
2. What is the PIN set before entering one time validation code ?
"0000"
Note - In devices from HTC and Sony matrix will be shown when Emergency Call window is opened on the lock screen.
Example :
Expression set in the application : a+b
Matrix on lock screen :
a1 b3 c4 d7
e2 f8 g2 h9
i5 j4 k1 l0
m1 n4 o6 p2
Now pin is a+b = 1+3 = 0004
Matrix on lock screen :
a2 b5 c1 d9
e7 f1 g2 h8
i2 j0 k5 l2
m8 n1 o7 p3
Now pin is a+b = 2+5 = 0007
If, E = a+b , S = {a , b , c ,d ,e } ,
V1 = { a = 1 , b= 2 , c = 9 , d = 5 , e = 2 } , Password = 3 ;
V2 = { a = 0 , b= 5 , c = 11 , d = 3 , e = 8 } , Password = 5 ;
Possible expressions from first password evaluation are
a+b
d-e
c-d-1
c%6
On cross checking with second password evaluation c-d-1 wipes out but still other expressions are valid. Complexity of deduction depends upon Expression and Values, but better than a static password .
update
Predfined expression list is updated
Recovery options are added.
Installation video added.
App got reviewd here...
http://gs4.wonderhowto.com/how-to/s...hematical-expressions-your-galaxy-s4-0156432/
Installation procedure video.
https://www.youtube.com/watch?v=tmolzN3mrCo
Recovery options
There are two ways to store our encryption details to recover our forgotten expression.
1. Store in an email.
2. Store in external storage.
And we have to select our recovery choice . There are 2 recovery choices,
1. Show expression in Plain text after 3rd consecutive incorrect attempt.
2. Show expression in encrypted text after 3rd consecutive incorrect attempt.
On typing the pin incorrect for 3 consecutive times, based on earlier choice , Expression is displayed.
Decryption procedure :
Let the stored recovery details be
a = VAN
+ = L
b = S
c = J
2. Let the encrypted expression shown be
VAN L S
3. Forgotten expression is obtained by replacing the letters. Here VAN = a , L = + , S = b ,
Then forgotten expression is a + b .
Nice app for security.
Brilliant concept but......where is the app ???
App can be found on the Play Store
The app always opens when I enter my pin(I mean it shows in recent apps)
I really need some help...I didn't watch what I'm doing. My App is set to a+b and I enabled lockscreen security without watching what I'm doing. I umlocked it one time with 0000, and entered the validation code from the toast (0001). Then I turned on lockscreen security and locked my devide, but now it isn't showing a Matrix, just a field to enter my code. But what is the code?
My Device is an unrooted Nexus 7 running the stock rom.
Edit: Already solved it by changin the Pin through the Android Device Manager.
I really like this app. It's lightweight (much more than LockDown Pro) so it should theoretically be amazing fast?! I will give it a try.
The only negative point for now are the in-app purchases. Is there any possibility to offer a lite and a pro version? I wanted to use an own pattern but I dislike in-app purchases because I do not want to grant internet access
//edit
I've just 'tested' a security issue. I'm using PAC-Rom (Samsung Galaxy S3) and Nova Launcher. App locking works fine. But it's no problem to uninstall the app via launcher (directly from home screen and/or from menu). I tried to lock 'settings', 'settings storage', 'nova launcher', 'nova launcher prime' but the problem still occurs. After uninstalling the app you can enter all locked apps without entering any password.
Not too savvy here, but how does one purchase the basic pack? I can't lock more than 3 apps.
Not working on my device. I cant open this app, after opening, just black screen that I get.
Brilliant app!
Sent from my beastly SM-T320
First of all I'd like to thank you for the app. I find that the concept is really great and that it has a lot of potential.
Having said that I think there are a couple of security concerns:
The ability to set a mathematical expression to calculate your acess pin is perceived, in my opinion, as a high security feature. I have a feeling though that it wouldn't be as secure as one may think since it's highly dependant of the expression one chooses.
Here's why:
Assumption: the chosen expression must be simple enough that the user can calculate the result quickly, accurately and without the need of a calculator.
Therefore we assume the user would chose expressions like: a+b+c; a+b-c; a * b - c; a *b + c
Since the numbers associated with each letter are within 0-9 this limits the result to a couple hundred different possible PIN numbers. We are in fact making our pin numbers easier to guess.
Example: Say I choose an expression such as a+b+c. Possible PIN numbers range from 0000 to 0027 no matter what numbers appear in the matrix.
The fact that the matrix changes after each attempt does improve the security but should any user set a simple expression (such as a+b) it's still quite possible to guess that PIN number with a bit of luck.
Possible solution: users should be advised to set easy to calculate and high complexity expressions.
Example: 1000 * a + 100 * b + 10 * c + min( 2*d; 9). it gives a highly variable result (0000-9999) with minimal calculation. Your pin is (a b c d) should d be less or equal than 4 and (a b c 9) should d be higher than 4.
Feel free to comment.
Thanks again for the app.
PROBLEM!
I enabled the Screen Lock and prior to that I validated and confirmed that I was able to see the matrix on the Emergency dialer.
Now my screen is locked and I cannot see the emergency dialer at all.
And I have my camera on lockscreen disabled too.
---------- Post added at 12:25 PM ---------- Previous post was at 12:20 PM ----------
Never mind. I started trying different combinations and I guess I got lucky on my third try with 0001 Lol
But yes, this is a brilliant app. Would love to have this issue fixed and it would be great if we can have the matrix toast on the lockscreen itself instead of the Emergency Dialer.
PROBLEMS
Great App, I have 2 suggestions.
There is a problem where I get a prompt to type the password randomly. For example when I swype to unlock the screen I get the prompt out of nowhere , or when exiting an app I get asked for the code.
2nd problem is that sometimes there are no numbers next to the letters , just a 0.
syedtahir16 said:
I enabled the Screen Lock and prior to that I validated and confirmed that I was able to see the matrix on the Emergency dialer.
Now my screen is locked and I cannot see the emergency dialer at all.
And I have my camera on lockscreen disabled too.
Click to expand...
Click to collapse
Same here. No toast ist shown on Emergency Dialer, but it worked during the verification process.
Unfortunately I'm not that lucky. I haven't figured out the right code yet.
Is there another way to disable the lock?
Edit:
Ok, I got it. I thought I tried every number, but I think mistyped the pin.
But there must be some bug/reason why the toast ist not show at multiple users...