C programming

C programming tutorial
A Short Guide On C Programming:
Contents
  1. Introduction
  2. What Is C
  3. Comparing C To Other Languages
  4. C & C++
  5. What Compiler Should I Use?
  6. Setting Up Your Compiler
  7. Your First Program
  8. Leaving Comments
  9. Error Debugging
  10. Variables and Constants
  11. Mathematical And Logical Operators
  12. Input and Output
  13. Functions
  14. Things You Must Remember
  15. Books I Recommend
  16. Bug Buster
  17. Answers
  18. Conclusion


INTRODUCTION:

I've seen a lot of people on forums i post on asking information on C programming because there interested in learning, it normally takes a few posts for people to point them in the right direction, i decided to write this tutorial/information text because there are very few of them on the internet (that i have seen) and i hope that this tutorial/information text is more helpful to the beginner programmer than other tutorials and such that are out there, keep in mind this is only a short guide to get you started.
This tutorial/information text was written by Vikas Nale!

WHAT IS C:

C is a medium-low level programming language that was originally developed by Dennis Ritchie at Bell Telephone Laboratories in 1972.
The language was created to design the UNIX operating system which was a lot more popular in 1972 than Windows, well actually Windows didn't even exist at that time.
Because C was such a powerful programming language it became widely used and people started making all sorts of programs with it.
C is called C because its predecessor was called B, believe it or not there is actually a language called D, i haven't bothered to check it out though, not many people code in it.
C is most defiantly the most used programming language in the world today.


COMPARING C TO OTHER LANGUAGES:

You may be thinking why should i learn C?
Well there are many reasons, first comparing C to Visual Basic, when comparing C to Visual Basic, C should be your choice if you are looking to get really stuck into programming Visual Basic programs are quite bloated and often need extra .dll files in order for certain parts of them to run on certain computers, including these files in Visual Basic applications can be a problem and of course makes the program larger than it needs to be.
When comparing C to Delphi, C should be your choice once again, because Delphi isn't no where near as popular as C and books and source code examples and books for the language will be harder to find.
The only other language apart from C and C++ you might be considering is ASM, there's nothing wrong with ASM and its better than C, however ASM is a very difficult language to learn, and to code complex programs it takes a lot longer than if you were to make that program in C, C should be your programming language of choice, below I've listed the pros and cons of each popular programming language.

Visual Basic 6:

Pros: By far the easiest language to program in, simple program creation makes Visual Basic a breeze to program in, lots of source code and books on the internet available for Visual Basic programmers.

Cons: Visual Basic programs sometimes require extra .dll files to be included with applications, Visual Basic is not a portable language and can only be used on Windows.


Delphi:

Pros: Quite easy to program in, not extra .dll files needed.

Cons: Not a very popular programming language.


C & C++:

Pros: Probably the most used program language out there, quite easy to learn and is what is considered a standard programming language, most programs you use are coded in C even C Compilers are coded in C.
Lots of source code available for C programs.

Cons: There aren't really any


ASM:

Pros: The lowest level programming language there is (except hexadecimal and binary.)

Cons: ASM is by far the hardest language out there, and coding is time consuming, coding a decent GUI would be very difficult.


C & C++:

I'm sure you would of heard of C and C++, and I'm sure your thinking what is the difference between the two languages.
C++ is an improved version of C, C++ is based around Object Oriented Programming, you cannot learn C++ with out learning C.
Despite the fact C++ came out, a lot of people still prefer to code in C rather than C++ and C is still the favorite among programmers, C is actually a newer programming language than C++, as the latest version of C was made in 1997 and C++ was made in the 1980's.
C++ is ment to be an improved version of C, as you might already know ++ in C programming is for incrementing, so C++ means an improved version of C.
If you were to program something in C++ instead of C you would be using OOP, where you program the program around the data it will or does hold.
If your going to learn a programming language for a job, you will be wanting to learn C++ as well as C, and maybe even C# which is Microsoft's programming language for the .NET operating system (code name longhorn.)


WHAT COMPILER SHOULD I USE:

There are many compilers out there you could use, some popular ones are LCC W32, Dev C++ and Visual C++
Out of all of these i recommend LCC W32, this tutorial is based on LCC W32 however you should still understand this tutorial even if your using another compiler, because this is a C tutorial, and programming has little to do with what compiler your using.
I have not tried Visual C++, but i do know its expensive, Dev C++ i had problems with, when i tried to compile certain code for some reason it just wouldn't compile, so of course that's why I'm using LCC W32.
Search Google for LCC W32 and you should find a download site, its freeware so there's no need to buy it or open your web browser to http://astalavista.box.sk or a similar warez/crack site.


SETTING UP YOUR COMPILER:

For those of you who aren't that computer literate, i will go through how to start a Project in LCC W32, step by step.

1. Open up LCC W32
2. Go to File, New, Project
3. It should came up with a menu where you can type certain information, e.g. Project Name.
4. Enter your project name (it can be anything, it doesn't matter.)
5. In "Sources: Working Directory" put the location of the folder where you want your binary to be compiled and your source file (example.c) to be saved to, as with the project name this can be anything you like (anywhere on your hard drive.)
6. Click in the last box (Objects and Executables), you should notice LCC W32 should automatically create a location, it's best just to leave it at that, unless you want to save your binary (compiled versions) somewhere easier to find.
7. Go to Create
8. It should then ask you if you want to generate the application skeleton, Click NO.
9. It should then bring up a screen where you can save your .c file (where your code is going to be saved) name this file what ever you want, although i must note if you save it as example123.c then when you first compile the binary it will be compiled as example123.exe
10. Another screen should come up, click Ok.
11. Another screen should come up with lots of information that will probably confuse you, just leave it as it is and click Next.
12. Another screen should come up, here you might want to change the output file name, the output file naming being the name of the executable when you compile it, under Type of Output you should change it to Console Application, because your a beginner C programmer, you won't want to jump into coding a GUI.
13. Click Next, then click Next again.
14. You should now have a white field where you can type your code, congratulations, you have now setup your compiler for use.


YOUR FIRST PROGRAM:

#include <stdio.h>

int main()

{

printf("Hello Aelphaeis");

return 0;

}

Now whack that into your compiler and hit compile.
You have now compiled your first program, traditionally most C Programmers first program is "Hello World" however i thought "Hello Aelphaeis" sounded a bit cooler.
Now ill explain what each part of the code does:

On the first line you have #include <stdio.h> this tells the compiler when compiling to include stdio.h header files in your application, stdio.h is needed for output to the screen.

On the second line you will see int main(), now this section of code is in virtually every C program there is, main() is the main part of the program, int is put before main() to tell the compiler the main() function will only return an integer (int = integer.)

You will notice on the 3rd line and last line there is "{" and "}" these brackets signal the beginning and end of a function, all functions begin with { and end with }.

On the fourth line you should see printf("Hello Aelphaeis");
printf is a function built into C, its a function that prints text to the screen or other output device (output device is usually the screen.)
"Hello Aelphaeis" is the text inside, notice it's in quotation marks, meaning it's NOT a variable it's actually a text string.
And of course last you will notice the semicolon, a semicolon tells the compiler that, that's the end of the command, generally semicolon's are on the end of each line of code.
However you would NOT put a semicolon after int main()

Last of all you should notice return 0;, this tells the compiler that the function main() will return nothing to the function that called it, however no function called it (although that doesn't matter), because return 0; is there the compiler knows the function will not return any value (all functions have to have a return or at least "return 0;".)


LEAVING COMMENTS:

When programming, sometimes you may want to make your program open source, and then of course other people are going to be downloading your code, now if there going to download your code they want to know what it does, and of course don't like to look through the code line by line to find out what it does, what can you do about that? (rhetorical question of course) You can leave comments in the code for them to read an example would be.

/* This is a Hello Aelphaeis Program */
#include <stdio.h>

int main()

{
printf("Hello Aelphaeis");
return 0;
}

See

/* This is a Hello Aelphaeis Program */

Anything between the /* */ is a comment, this comment can also be multi-line another way of leaving a comment in is using
//example of comment in code
Although i must note that method isn't used very often and is discouraged by some programmers (don't ask me why.)
And that's basically how to leave comments in your code for other people to read.

Tip: Do not leave to many comments, only a few that explain what the hard to understand parts of the program do.



ERROR DEBUGGING:


#include <stdio.h>

int main()

int age

{

printf("Enter Your Age:");
scanf("%d", &age)
printf("Your age is %d", age);

return 0;

}

Put that into your compiler and hit compile, you should notice LCC W32 should come up with the following error message:

Error: C:\aelphaeis\aelphaeis.c 10 Syntax error; missing semicolon before "printf"

Now what does that tell you? If you don't know click on the error message, it should highlight a line, it's telling you there is a missing semicolon before that line, look if you didn't already notice it, you should notice there is a missing semicolon after:
scanf("%d", &age)
Put the missing semicolon in at the end of it and hit compile, it should of compiled and fine, and you should of learnt the basics of error debugging, one thing you must remember the compiler doesn't always pin point exactly where the error message is, so you have to pin point it yourself sometimes.
Error reports in LCC W32 are great, because they tell you a bit about what is wrong with the code, although as i said sometimes you have to look hard before you notice the error, also you find a lot of the time fixing up one error will sometimes fix up all the other error messages you get from LCC W32.
You know what "printf("Enter Your Age:");" does don't you?
I'm sure your wondering though about the line below it and "int age"
well first ill explain "int age", that basically declares the word "age" as an integer variable (variable is basically where data can be stored.)
scanf("%d", &age) is a bit more complicated, scanf is a function built into C which takes input from the keyboard (or other input device) and places it inside a variable.
"%d" basically means to put the received data into to an integer variable and &age tells the compiler that the received data that is put into %d% should be put into the variable "age" which if you have a decent memory we declared was an integer variable at the beginning of the program.
So basically after scanf("%d", &age); is completed, the number the person entered is now stored in the integer variable "age" then you have the next line of code:
printf("Your age is %d", age);

You should understand what that does, if not like with scanf you have a %d in there, telling the program that "%d" is an integer variable, then after that you have a comma then "age" which is the variable that is printed to the screen.
If you were to put:
printf("Your age is %d %d %d", age, age, age);

That would print the number 3 times, for each %d you have you have to put a variable to be printed after the comma in the bracket.
If you were to have the following code:


#include <stdio.h>

int age;
int mum;

int main()
{
printf("Enter Your Age:");
scanf("%d", &age);
printf("Enter Your Mum's Age:");
scanf("%d", &mum);
printf("Your age is %d and your Mum's age is %d", age, mum);
return 0;
}

Notice how in the line:
printf("Your age is %d and your Mum's age is %d", age, mum);
You have two %d, you may be confused, what the program does is, first prints %d the first %d it prints if the first variable after the semicolon, you will notice the integer variable age is first, so it prints that, then when it comes along to the next %d it looks for the second variable to print, which of course is the integer variable "mum"
When printing variables you must remember the spelling has to be correct and the case does also, if you were put have.
printf("Your age is %d and your Mum's age is %d", age, MUM);
You would notice your compiler would generate two error messages,

Error: C:\aelphaeis\aelphaeis.c; 12 undeclared identifier 'MUM'
Error: C:\aelphaeis\aelphaeis.c 12 possible usage of 'MUM' before declaration.

If you click on the error message you should notice it highlights the line, from the error message you should be able to interpret what is wrong, it says undeclared identifier, but we declared the variable mum didn't we?
Of course what is wrong is that the word "mum" is in the wrong case, so the compiler generated an error, and of course you and all the other programmers out there are lucky we have this sort of feature in compilers, because you may perform a typo and not even notice it, all you have to do is change the "MUM" to lowercase so the program understands its the "mum" variable and not some other variable.
You should notice if you fix up the error and compile, there are no error messages, before there were two error messages, fixing one part of the code got rid of both of them, of course when programming if you get a lot of errors, the chances are there are a few bugs in your code, not just one.



VARIABLES AND CONSTANTS:

You already know what a variable is, however you do not know about different variables and the difference between them, you also don't know what constants are, so let's first take a look first at different type of variables.
Different variables are used for different purposes, if you wanted to store numbers in something you would of course use an integer (assuming the number wasn't to large and didn't have decimal points.)

int (integer):

int (integers) can be declared simply by doing

int name;
An integer can hold any number from -32768 to -32767, generally integers should be used for any basically calculation.
Integer variables do not have decimal points.

short (short integer):

This is exactly the same as an int, you might be thinking well why the hell is there two of them then?
Well on very old computers there is a difference between the two, however on all modern computers int and short are the same thing, it's best just to use int, because int is more widely used than short.
You can declare a short integer by:
short name;

float:

A float variable can hold 1.2E-38 in other words when using very large numbers you will be wanting to use a float, or if your using numbers with decimal points you will also be wanting to use a float variable.
float variables can be declared by doing:
float name;

char(character):

char variables are usually used to hold letters and numbers, char variables can only hold one character at a time, so if you wish to store a word inside a char variable you will have to use the variables indexes (not covered in this guide.)
character variables can be declared by:
char name;

long (long integer):

A long integer is just like a normal integer but it can hold more data than a normal integer (incase you haven't already guessed.)
A long integer can hold between -2,147,483,648 and 2,147,438,647.
You can declare a long integer by:
long name;




unsigned char (Unsigned Character):

unsigned character variables can hold any character from 0 to 255, in other words basically all the characters there are really.
You can declare an Unsigned Character by:
unsigned char name;

unsigned int(Unsigned integer):

An unsigned integer can hold any number from 0 to 65535 you can declare an unsigned integer by:
unsigned int name;

unsigned short(Unsigned short integer):

I shouldn't need to tell you this is exactly the same as unsigned int, except on old computers or systems that aren't very popular.

unsigned long(Unsigned long integer):

A unsigned long integer can hold all numbers from 0 to 4,294,967,295
This variable should be used to hold large numbers.
This can be declare by:
unsigned long name;

double(Double Precision):

A Double Precision variable can hold between 2.2E to 308.
In other words you can store very large numbers in a Double Precision variable.
  

You can also use these variables in constants, you should make sure you use the appropriate variable though for holding the appropriate data, even if you can hold a small number in a larger variable it's best not to, that way your program will be a lot more efficient and use up less RAM.
Below is some code that demonstrates variables and constants:

#include <stdio.h>
/* Aelphaeis 0wnz j00 */
#define pi 3.14
int diameter;
int answer;
int main()
{
printf("Enter the DIAMETER of your circle:");
scanf("%d", &diameter);
answer = diameter * 2 * pi;
printf("Circumference is: %d", answer);
return 0;
}

On the first line we have #include <stdio.h> if you have a decent memory you should remember what that does, it includes header files needed for output to the screen.
Below that we have /* Aelphaeis 0wnz j00 */ which is just a comment, telling you that i 0wn, lol.
Then on the third line we have #define pi 3.14, what this does is declare "pi" as a constant, a constant which is equal to 3.14, which you should know if you attended school regularly is PI.
Below that is

int diameter;
int answer;

This is declaring diameter and answer as integer variables.
Then we have int main() which of course is the main part of the program, the first line inside that main() is
printf("Enter the DIAMETER of your circle:");
That simply prints information to the screen, asking the user to input the diameter of his or her circle.
scanf("%d", &diameter);
I hope you remember what that does, scanf is used for receiving information from the input device connected to the computer, which in most cases should be a keyboard, inside the brackets we have "%d", &diameter, %d means an integer variable, after that is a comma then &diameter which means the value stored in %d will be transferred to the variable diameter.
answer = diameter * 2 * pi;
Basically the CPU will work out diameter(number stored inside variable) multiplied by 2 then multiplied by PI, then it will store the answer inside the integer variable answer.
I also must not forget to mention that there is no difference between
answer = diameter * 2 * pi;

and

answer = diameter*2*pi;
White space does not matter to your compiler, however will be formatted accordingly when you save your work as a .c file.
The last important line we have is
printf("Circumference is: %d", answer);
Which prints "Circumference is:" and then the answer, if you look you will see %d again, which of course means there will be an integer printed to the screen (because of the printf command before it) and then after the text is a comma then answer which is the variable which holds the answer to the problem, if you don't understand what i just said, you might want to carefully look through the code again.
If you compile the program and then test it out, you should notice the answer it returns is a whole number and will have no decimal points it doesn't take a genius to figure out why that is, incase you don't know its because the variable was stored inside an integer which of course cannot hold decimal points, if you wanted to have decimal points in there you would have to use another variable like float.
Now you should have a fair idea of what variables and constants are and how to use them.
To sum the following part of this text up, variables are for storing information in RAM, there an allocation of memory where you can store data, a constant is a variable that once declare cannot be changed, and constants are probably mostly used in mathematical calculations.
There is something important i must note as well, there is a difference if you declare a variable outside of a function and inside, if your programming and your using a variable, if the variable is only needed within one function it is best just to declare and initialize that variable in that function, if the variable is going to be used in multiple functions then you would use what is called a Global Variable which is where the variable is declared under the #include tags and can be used in any functions, although you can use global variables for everything it is strongly recommended that you do NOT because it makes your coding look sloppy and all professional programmers stay away from using too many Global Variables.
When declaring variables it is important to declare a legal variable name below are some rules to use when declaring a variable.

1. The name can only contain letters, digits and underscores "-"
2. The first character of the name must be a letter.
3. When using variables in programming the case of each letters counts, for example test1 is different to Test1.
4. The variable can NOT be one of C's keywords e.g. long int.
When declaring a variable it's best to name it what relating to what ever information it is going to hold (can't be a C keyword though.)
Below are some illegal and legal C variable names (examples.)

long - illegal, one of C's keywords

hello - legal

test# - illegal, contains illegal character

123test - illegal, first character is a number

xxx_yyy - legal, pretty stupid name though.



Using typedef:

Are variable keywords hard to remember?
Well you no longer have to worry, because of a function C has built in called typedef.
Let's just say you wanted to use something else instead of int to declare a integer variable, using typedef you could do:

typedef int integer;

You could then use the word integer instead of int.
So if you were to declare a variable as an integer you could do:

integer example;








MATHEMATICAL AND LOGICAL OPERATORS:

While programming your obviously at some point going to program program's that require users to enter information, and of course this information will be compare to other information as well as things that you define in your program.
This chapter will also introduce you to the
if (x == y) statement.

Below is a program that compares two numbers entered by a user:


#include <stdio.h>
int one1;
int two2;

int main()
{
printf("Enter 2 Numbers:");
scanf("%d", &one1);
printf("Enter a second number:");
scanf("%d", &two2);

if (one1 > two2)
      printf("First number is larger");
      else
      printf("Second number is larger");

return 0;
}

You should know what each part of the code does, except for maybe:

if (one1 > two2)
      printf("First number is larger");
      else
      printf("Second number is larger");

Basically what this does is, if the first variable which is one1 is larger than two2 then it prints "First number is larger", that if it's true, if it does not evaluate to true then

else
printf("Second number is larger");

So now you should know basically how to compare two variables.
Let's now alter the code for it to compare something a different way.










#include <stdio.h>
int one1;

int main()
{
printf("Enter your age:");
scanf("%d", &one1);

if (one1 > 16)
      printf("Your older than Vikas Nale");
      else
      printf("In j00 face I'm older than you!");

return 0;
}

What this does is ask the user for there age, then compares it to a number instead of comparing it to another variable.
Let's just alter that code again (the last part) so it does something slightly different.

if (one1 == 16)
      printf("Your the same age as me");
      else
      printf("Your not the same age as me");

What the above code does is check if the user enter 16, notice it uses "==" and not "=" in C programming = places information from one variable into another, if you wish to compare something you have to use "=="
The Mathematical Operators used in C are:

Equal "=="
Greater than ">"
Less than "<"
Greater than or equal to ">="
Less than or equal to "<="
Not equal "!="

Try making some short programs using these Mathematical Operators.


So now you know about Mathematical Operators you would want to be able to use them with more flexibility this is where Logical Operators come into play.

AND  &&
OR   ||
NOT  !

So now you know what they are, below is an example program where one or more of the Logical Operators are used.




#include <stdio.h>

int one1,two2;

int main()

{
      printf("Enter a god damn number:");
      scanf("%d", &one1);
      printf("OK, now enter another:");
      scanf("%d", &two2);
      if (one1 && two2 == 5)
      printf("Both numbers equal 5");
      else
      printf("One or both of the numbers do not equal 5");
      return 0;
}

If you look at the program you should be able to see what it does, if not well maybe you should of been reading the rest of this book a bit better, but anyway i will explain it to you.

int one1,two2;

Declares one1 and two2 both as integer variables.
Then you have
printf("Enter a god damn number:");
Which asks the user to enter a number, then below that
scanf("%d", &one1);

Notice the %d, that means the data entered will be stored as an integer, then you have a comma and then &one1 which stores the information inside the variable one1.
Then we have the part which compares the two numbers.
if (one1 && two2 == 5)

That basically means if the variable one1 and the variable two2 equals 5 then execute the following code:
printf("Both numbers equal 5");

If not (else) execute this code:

printf("One or both of the numbers do not equal 5");

Then of course you have the

return 0;

At the end of the code, telling the program to return 0, in other words NOTHING.

Now that you know how to use the AND operator you should be able to also use the OR operator "||" with out quotation marks that is.




Lets now have a play around with "!" which if you have a decent memory you should know means NOT.
Examine the following program:

#include <stdio.h>

int Aelphaeis;

int main()

{
printf("Enter a number:");
scanf("%d", &Aelphaeis);

if (Aelphaeis != 5)
printf("The number you entered is NOT 5");
else
printf("The number you entered IS 5");
return 0;
}

If you examine that code you should realize what it does, you notice
if (Aelphaeis != 5)
And think hey why isn't that
if (Aelphaeis !== 5)
When using "!" you do not have to do double equal signs.
You could also change != to something like !=> 5 , meaning not larger than 5.

You now should know about the if, else statement as well as AND, OR, NOT and equal to, not equal to, greater than, less than, greater than or equal to or less than or equal to.
For some tasks it's best to use C's conditional operator "?" instead of the if statement, this is quite basic to use and i will explain below.


example:

z ? 100 : 500

The above means, if z is true (meaning z actually contains something higher than 0) then z = 100 else z = 500.
It would be similar to the following if statement.

if (z)
z = 100
else
z = 500

But using C's conditional operator is a shorter way of doing it.

Adding Subtracting & Incrementing, Decrementing:

During programming it's more than likely for one reason or another you will want to increase of decrease a number of alter it some how.
You can add, multiply, divide or subtract quite easily below is some code showing an example.
#include <stdio.h>

int one1;
int two2;
int three3;
int four4;

int main()

{
      printf("Enter a number:");
      scanf("%d", &one1);
      one1 += 5;
      printf("That number plus 5 is: %d\n", one1);
      printf("Enter another number:");
      scanf("%d", &two2);
      two2 -= 5;
      printf("That number subtract 5 is: %d\n", two2);
      printf("Enter another number:");
      scanf("%d", &three3);
      three3 *= 5;
      printf("That number multiplied by 5 is: %d\n", three3);
      printf("Please enter one more number:");
      scanf("%d", &four4);
      four4 /= 5;
      printf("That number divided by 5 is %d\n", four4);

      return 0;

}

When you run that program you may notice it rounds off numbers, this is of course because we are using integer variables, if you wish for them not to round of use float variables, you would also have to change "%d" to "%f" because you would be inputting and outputting float variables.

Now you know how to use addition, subtraction, multiplication and division you should learn how to increment and decrement a variable.
Here is a very short program that shows you how to do this:

#include <stdio.h>

int x = 7

int main()

{
printf("Incrementing Number....");

x++

printf("%d", x);

return 0;

}


By analyzing the program, you could see x is declared as an integer, and at the same time it is also initialized, it's at initialization x is equal to 7, then you have the program print "Incrementing Number...." then it increments the number (x++) then prints the number.
If you wished to decrement x all you would have to do is x--.

Mathematical Operator Precedence:

In an expression that contains more than one operator the order of each calculation will be worked out by the operators precedence.
Below is a list showing the precedence of operators in C.

Level                Operator(s)

1                    () [] -> .
2                    ! ~ ++ -- *
3                    * (multiplication) / %
4                    + -
5                    << >>
6                    < <= > >=
7                    == !=
8                    & (bitwise AND)
9                    ^
10                   |
11                   &&
12                   ||
13                   ?:
14                   = += -= *= /= %= &= ^= |= <<= >>=
15                   ,

Although some operators take precedence over others some are on the same level as each other.

x = 3 + 3 * 4;

Would make x equal to 24, since multiply and addition are on the same level the line of code would mean, 3 + 3 = 6 then multiply 6 by 4 and store the value inside of x, which by the way you would want to make an integer.
If you were using lots of different operators and you wanted to work out a calculation with your own precedence so the calculation ends up being correct you can use parentheses to enclose bits of your calculation for example.

x = (4 * 5) + 6

The first thing the code would do is multiply 4 times 5 before adding 6 to it.
That's just a basic example, using multiple parenthesis you can co-ordinate the precedence of a calculation, for example:

x = 3 * (2 * (8 + (6 / 2)))

6 / 2 is deeply nested inside the parenthesis therefore it would be the first thing to be calculated by your computers CPU, after than 8 would be added to it, then it would be multiplied by 2 then the answer to the whole lot would be multiplied by 3 then the answer would be stored inside x, again you would want x to be an integer.


INPUT AND OUTPUT:


Well you should of learned about the basics of input and output, but to be able to do more programming of course you will need to know more about input and output, first we will start off explaining more on printf and scanf.



printf:

Ok printf is quite an easy function to use in C you know how to print text strings and you know how to even print integer variables, let's learn about printing other variables.

#include <stdio.h>

float x =10, y = 12;

int main()

{
      printf("x equals:%f\n", x);
      printf("y equals:%f\n", y);

      return 0;

You should be able to identify what the above code does, first we have the header file which is needed for output to the screen, then we have
float x = 10, y =12
This declares and initializes x and y and sets what data they contain.
The only other thing you should notice that is different its "%f", this is used in printf when you want to print a float variable to the screen.
There is one thing i most probably didn't mention earlier in this text, what if you wanted to write a very long sentence when writing your code but didn't want your save file to be very long in width.
You can use "\" to break lines while using printf below is an example:











#include <stdio.h>


void main()

{
      printf("Hello My Name Is Vikas Nale");
}




scanf:

You know how to print float variable to the screen, and I'm sure you could probably figure out how to store float variables using scanf just incase below is some example code:

#include <stdio.h>

float x,y;


int main()

{
      printf("Enter a number:");
      scanf("%f", &x);
      printf("Enter another number:");
      scanf("%f", &y);
      printf("Numbers you entered %f & %f", x, y);

      return 0;

}

You should notice if you compile that code and run it, that it prints out the two numbers you entered, if you entered 10 and 8 it would print them out as 10.00000 and 8.00000, this is because the variable you are using is a float variable and designed to hold large numbers, if your only wanting to hold small numbers with out decimal points it's best to use an integer variable, scanf can only be used for storing numerical data.
You know how to input and output float and integer variables using %f and %d, below i have listed the other Specifiers you can use to print other variables.


%c  char
%d  integer
%ld long integer
%f  float
%s  char string
%u  unsigned integer
%lu long unsigned integer

When printing out stuff using the examples in this text you may of noticed the \n which you can use to make a new line, and you probably already know what I'm going to say now, yes there are other things like \n you can use with printf below i have listed them.

\n New line
\b Backspace
\a Bell
\\ Backslash
\t Horizontal tab
\? Question mark
\' Single quote

Ok now that you know about this stuff let's make a small program to test it out.




#include <stdio.h>

void main()

{
      printf("\tHetrosexual\tHomosexual\n");
      printf("\tAelphaeis\tBrownsun\n");
      printf("\a\a\a\a\a");

}

You have of noticed, well you should of noticed in the first and second printf i used i used \t, \t puts things into columns, i made two columns one with Heterosexual and one with Homosexual then i put a name under each one.
Then under than i had \a\a\a\a\a which made your computer beep if you compiled and ran the code.

Using puts function:

The puts function is a bit like printf except it is used only when you want to output a text string with not variables, below is an example code for using puts.


#include <stdio.h>

void main()

{
puts("This was printed using");
puts("The puts function");




FUNCTIONS:

C is a modular programming language, which means it uses functions, not just functions that are built into C but also user defined functions, which if you don't already know are functions that are coded by the programmer.

Below is a simple example showing a function:

#include <stdio.h>

void example();

int main()

{
      printf("The next thing will be printed by a separate function\n");
      example();
      return 0;

}


void example()

{
      printf("This was printed by example");


}

Ok now i will explain the pieces of code that you haven't worked with before, the first bit that will seem unknown will be
void example();
Now this is the function prototype, function prototypes are always needed and are placed above all the other functions and should contain the type of variable it returns in the function prototype.
In the example code we had void example() this is because this function did not need to return any information to the function that called it or any other function (even though there were no other functions except main.)
Ok now that we know how to call on a function and make it execute code, let's now learn how to pass an argument to a function.

#include <stdio.h>

int half_of(int x);

int main()

{
  int x, y;
  printf("Please enter a number:");
  scanf("%d", &x);
  y = half_of(x);
  printf("Half of %d is %d", x, y);
  return 0;

}



int half_of(int x)
{


return (x/2);


}


Ok if you look at the code you should know basically what it does, i will explain the hard parts.
First we have
int half_of(int x);
This of course is the function prototype it declares that the function half_of can return an integer variable and that other functions can pass another integer variable(s) to it as an argument (int x) is the part that declares the variable that can be passed to it.
int x, y;
Declares x & y as integer variables.
printf("Please enter a number:");
Prompts the user to enter a number.
scanf("%d", &x);
Stores the entered number as an integer inside the variable x.
y = half_of(x);
Calls on the half_of function and passes the variable x to it, the returned data is stored in side the variable y.
printf("Half of %d is %d", x, y);
Prints the variable x which stores the original number the person entered, then prints the variable y which has the number which the half_of function return to it.
return (x/2);
Simply returns x divided by 2.


Ok now you know a bit about functions, let's take a look at a function which is a bit more complex than the ones we have already had a look at in this text:

#include <stdio.h>

int x, y;

int multiply(int x);

int main()

{
      printf("Enter a number between 1 and 10:\n");
      scanf("%d", &x);

      if( x > 10 || x < 1)
      {
            printf("Enter a number between 1 and 10 IDIOT!\n");
      }

      else

      {
            y = multiply(x);
            printf("Your number is %d", y);
      }

return 0;

}

int multiply(int x)

{
      if (x <= 5)
      {
      printf("Your number is less than 5\n");
      return x;
}
      else

      {
      x *= 10;
      printf("Your number is larger than 5 and for no reason has been multiplied by 10\n");
      return x;
    }

}


Now lets analyze this code.
On the first line we have the #Include which includes the header files needed for output to the screen.
Then we have int x, y which of course declares x and y as integer variables and below that we have a function prototype
int multiply(int x);
The function is called multiply it can return integer variables and one integer variable can be passed to it.
After the function prototype we have
printf("Enter a number between 1 and 10:\n");
scanf("%d", &x);

Which prompts the user to enter a number between 1 and 10 then stores the entry inside the integer variable x.
After the information is stored inside the variable the number is checked to see that it is NOT greater than 10 or less than 1, if either evaluates to true (|| = OR) then the following is printed to the screen:
Enter a number between 1 and 10 IDIOT!

If the number is between 1 and 10, the program then perform the following
y = multiply(x)
This passes the x variable to the function multiply, it is then returned and the returned data is then stored inside the integer variable y.
Now lets examine the multiply function:


if (x <= 5)
      {
      printf("Your number is less than 5\n");
      return x;
      }

Basically it checks if the number is less than 5, if true, it prints:
"Your number is less than 5" (with out quotation marks)
it then returns x and the main() function prints
Your number is: x (x being a variable.)
If the if statement evaluates to false then to program goes to
else

{
      x *= 10;
      printf("Your number is larger than 5 and for no reason has been multiplied by 10\n");
      return x;
}

This multiplies x by 10 (x *= 10) then prints:
"Your number is larger than 5 and for no reason has been multiplied by 10"

Then returns the variable x, which the program multiplied by 10, and then the main() function prints:
"Your number is: x" (x being a variable.)




THINGS YOU MUST REMEMBER:

1. A semicolon should go on the end of each line.
2. Semicolon's do not go on the end of the beginning of a function.
3. For every function you must have a function prototype.
4. Remember to use the right type of variables.
5. When programming it is essential to include the right #include tags.
6. You must declare a variable before you can use it.
7. When using scanf remember to use "&" before the variable.
8. C is a portable language, but sometimes you might have to alter your code a bit for it to run on another operating system.
9. When using variables with functions you must pass the variable to the function from the calling function to the function that needs it.
10. Global variables are good but you should only use them when you have to.
11. The include tags should go at the top of your code.
12. There is a difference between upper and lowercase variables in C.
13. Comments are helpful but you don't want them everywhere.
14. C source files should be saved as example.c
15. Most importantly C for some people is quite hard to learn, take your time reading tutorials and such on C, it will take a while before you really get into programming.
16. This is a just a short guide, after reading this read some of the books i recommend.


BUG BUSTER:

Now that you know the very basic's of C programming, it is time to test what you know below are some short programs, however this programs contain errors it is your job to fix up this programs using your basic programming knowledge.





1.

#include stdio.h

int main()

{
printf("Hello World")
return 0;
}


2.

#include stdio.h

int main()

{
printf(Please enter a number)
scanf("%d", hello)
return 0;
}

3.

#include stdio.h

char hello

int main()

{
printf(Please enter a number between 1 and 10)
scanf("%d", hello)
print();
return 0;
}

int print(int print);

{
printf("%d", hello)
return 0;
}



4.

include# stdio.h

void main()

{
printf(Enter a number)
scanf("%d", hello)
print(hello)
return 0;
}

char print(int x)
{
printf(x);
return 0;
}

Now IF you were able to fix up all the errors in the above programs, you have successfully studied this guide, and you can now move on to a more advanced guide.
If not you might want to read through this text again and study it more heavily.


ANSWERS:

For those of you who just can't manage to find out what is wrong with one or more of the programs, below i have listed the errors in each one.


1.

1. No triangular brackets surrounding stdio.h
2. No semicolon after printf

2.

1. No triangular brackets surrounding stdio.h
2. No semicolon after printf
3. No quotation marks before and after text in printf
4. Now ampersand (&) before variable hello
5. Variable hello is not declare as an integer

3.

1. No triangular brackets surrounding stdio.h
2. hello should be declared as an integer
3. No quotation marks before and after text in printf
4. No semicolon after printf
5. Now ampersand (&) before variable hello
6. No semicolon after scanf
7. Function print does not have a prototype
8. The function print, it's start:
int print(int print)
Should NOT have a semicolon after it.
9. Not semicolon after printf in print function

4.

1. # is after include
2. stdio.h is not surrounded by triangular brackets
3. Should be int main() not void main()
4. No quotation marks in printf
5. No semicolon after printf
6. No semicolon after scanf
7. No ampersand (&) before hello
8. hello is not even a declared variable, should be declared
9. No semicolon after print(hello), incase your confused what this does is pass the variable hello to the function print, it's not ment to be printf.
10. char print should be int print
11. The function print has no prototype



BOOKS I RECOMMEND:

Primers Guide To C
Teach Yourself C In 21 Days
Practical C Programming, 3rd Edition
The C Programming Language

CONCLUSION:

I hope this text was of help to you and you enjoyed it, you should now make up your mind whether or not C is the right language for you, now that you know the very basics of C.
Maybe one day i will write a full guide to C programming.

GREETZ TO:

htek, The Goon Squad(TGS-Security.com), syst3m 0f cha0s, The Media Assassins, Read101, HackJoeSite and Tomchu.


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1 comments : on " C programming "

Ferris said...

hiii

nice blog and good conten

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