C Programming Example

C programming examples: These programs illustrate various programming elements, concepts such as using operators, loops, functions, single and double dimensional arrays, performing operations on strings, files, pointers etc. Browse the code from simple c program to complicated ones you are looking for, every one of them is provided with output. C program download with executable files, so that you save on your computer and run programs without compiling the source code. All programs are made using c programming language and Codeblocks, most of these will work under Dev C++ compiler also. Download software you need to develop codes. The first program prints "Hello World" on screen.

Basic Data Type And Operators

The type of a variable determines what kinds of values it may take on. An operator computes new values out of old ones. An expression consists of variables, constants, and operators combined to perform some useful computation. In this chapter, we'll learn about C's basic types, how to write constants and declare variables of these types, and what the basic operators are.
As Kernighan and Ritchie say, ``The type of an object determines the set of values it can have and what operations can be performed on it.'' This is a fairly formal, mathematical definition of what a type is, but it is traditional (and meaningful). There are several implications to remember:

1. The ``set of values'' is finite. C's int type can not represent all of the integers; its float type can not represent all floating-point numbers.
2. When you're using an object (that is, a variable) of some type, you may have to remember what values it can take on and what operations you can perform on it. For example, there are several operators which play with the binary (bit-level) representation of integers, but these operators are not meaningful for and may not be applied to floating-point operands.
3. When declaring a new variable and picking a type for it, you have to keep in mind the values and operations you'll be needing.

In other words, picking a type for a variable is not some abstract academic exercise; it's closely connected to the way(s) you'll be using that variable

Introdution to C

This tutorial is designed to be a stand-alone introduction to C, even if you've never programmed before. However, because C++ is a more modern language, if you're not sure if you should learn C or C++, I recommend the C++ tutorial instead, which is also designed for people who have never programmed before. Nevertheless, if you do not desire some of C++'s advanced features or simply wish to learn C instead of C++, then this tutorial is for you! 

Getting set up - finding a C compiler

The very first thing you need to do, before starting out in C, is to make sure that you have a compiler. What is a compiler, you ask? A compiler turns the program that you write into an executable that your computer can actually understand and run. If you're taking a course, you probably have one provided through your school. If you're starting out on your own, your best bet is to use Code::Blocks with MinGW. If you're on Linux, you can use gcc, and if you're on Mac OS X, you can use XCode. If you haven't yet done so, go ahead and get a compiler set up--you'll need it for the rest of the tutorial.

Intro to C

Every full C program begins inside a function called "main". A function is simply a collection of commands that do "something". The main function is always called when the program first executes. From main, we can call other functions, whether they be written by us or by others or use built-in language features. To access the standard functions that comes with your compiler, you need to include a header with the #include directive. What this does is effectively take everything in the header and paste it into your program. Let's look at a working program:

#include <stdio.h>
int main()
{
    printf( "I am alive!  Beware.\n" );
    getchar();
    return 0;
}

Let's look at the elements of the program. The #include is a "preprocessor" directive that tells the compiler to put code from the header called stdio.h into our program before actually creating the executable. By including header files, you can gain access to many different functions--both the printf and getchar functions are included in stdio.h. 

The next important line is int main(). This line tells the compiler that there is a function named main, and that the function returns an integer, hence int. The "curly braces" ({ and }) signal the beginning and end of functions and other code blocks. If you have programmed in Pascal, you will know them as BEGIN and END. Even if you haven't programmed in Pascal, this is a good way to think about their meaning. 

The printf function is the standard C way of displaying output on the screen. The quotes tell the compiler that you want to output the literal string as-is (almost). The '\n' sequence is actually treated as a single character that stands for a newline (we'll talk about this later in more detail); for the time being, just remember that there are a few sequences that, when they appear in a string literal, are actually not displayed literally by printf and that '\n' is one of them. The actual effect of '\n' is to move the cursor on your screen to the next line. Notice the semicolon: it tells the compiler that you're at the end of a command, such as a function call. You will see that the semicolon is used to end many lines in C. 

The next command is getchar(). This is another function call: it reads in a single character and waits for the user to hit enter before reading the character. This line is included because many compiler environments will open a new console window, run the program, and then close the window before you can see the output. This command keeps that window from closing because the program is not done yet because it waits for you to hit enter. Including that line gives you time to see the program run. 

Finally, at the end of the program, we return a value from main to the operating system by using the return statement. This return value is important as it can be used to tell the operating system whether our program succeeded or not. A return value of 0 means success. 

The final brace closes off the function. You should try compiling this program and running it. You can cut and paste the code into a file, save it as a .c file, and then compile it. If you are using a command-line compiler, such as Borland C++ 5.5, you should read the compiler instructions for information on how to compile. Otherwise compiling and running should be as simple as clicking a button with your mouse (perhaps the "build" or "run" button). 

You might start playing around with the printf function and get used to writing simple C programs.

Explaining your Code

Comments are critical for all but the most trivial programs and this tutorial will often use them to explain sections of code. When you tell the compiler a section of text is a comment, it will ignore it when running the code, allowing you to use any text you want to describe the real code. To create a comment in C, you surround the text with /* and then */ to block off everything between as a comment. Certain compiler environments or text editorswill change the color of a commented area to make it easier to spot, but some will not. Be certain not to accidentally comment out code (that is, to tell the compiler part of your code is a comment) you need for the program. 

When you are learning to program, it is also useful to comment out sections of code in order to see how the output is affected.

Using Variables

So far you should be able to write a simple program to display information typed in by you, the programmer and to describe your program with comments. That's great, but what about interacting with your user? Fortunately, it is also possible for your program to accept input. 

But first, before you try to receive input, you must have a place to store that input. In programming, input and data are stored in variables. There are several different types of variables; when you tell the compiler you are declaring a variable, you must include the data type along with the name of the variable. Several basic types include char, int, and float. Each type can store different types of data. 

A variable of type char stores a single character, variables of type int store integers (numbers without decimal places), and variables of type float store numbers with decimal places. Each of these variable types - char, int, and float - is each a keyword that you use when you declare a variable. Some variables also use more of the computer's memory to store their values. 

It may seem strange to have multiple variable types when it seems like some variable types are redundant. But using the right variable size can be important for making your program efficient because some variables require more memory than others. For now, suffice it to say that the different variable types will almost all be used! 

Before you can use a variable, you must tell the compiler about it by declaring it and telling the compiler about what its "type" is. To declare a variable you use the syntax <variable type> <name of variable>;. (The brackets here indicate that your replace the expression with text described within the brackets.) For instance, a basic variable declaration might look like this:

int myVariable;

Note once again the use of a semicolon at the end of the line. Even though we're not calling a function, a semicolon is still required at the end of the "expression". This code would create a variable called myVariable; now we are free to use myVariable later in the program. 

It is permissible to declare multiple variables of the same type on the same line; each one should be separated by a comma. If you attempt to use an undefined variable, your program will not run, and you will receive an error message informing you that you have made a mistake. 

Here are some variable declaration examples:

int x;
int a, b, c, d;
char letter;
float the_float;

While you can have multiple variables of the same type, you cannot have multiple variables with the same name. Moreover, you cannot have variables and functions with the same name. 

A final restriction on variables is that variable declarations must come before other types of statements in the given "code block" (a code block is just a segment of code surrounded by { and }). So in C you must declare all of your variables before you do anything else: 

Wrong

#include <stdio.h>
int main()
{
    /* wrong!  The variable declaration must appear first */
    printf( "Declare x next" );
    int x;

    return 0;
}

Fixed

#include <stdio.h>
int main() 
{
    int x;
    printf( "Declare x first" );

    return 0;
}

Reading input

Using variables in C for input or output can be a bit of a hassle at first, but bear with it and it will make sense. We'll be using the scanf function to read in a value and then printf to read it back out. Let's look at the program and then pick apart exactly what's going on. You can even compile this and run it if it helps you follow along.

#include <stdio.h>

int main()
{
    int this_is_a_number;

    printf( "Please enter a number: " );
    scanf( "%d", &this_is_a_number );
    printf( "You entered %d", this_is_a_number );
    getchar();
    return 0;
}

So what does all of this mean? We've seen the #include and main function before; main must appear in every program you intend to run, and the #include gives us access to printf (as well as scanf). (As you might have guessed, the io in stdio.h stands for "input/output"; std just stands for "standard.") The keyword int declares this_is_a_number to be an integer. 

This is where things start to get interesting: the scanf function works by taking a string and some variables modified with &. The string tells scanf what variables to look for: notice that we have a string containing only "%d" -- this tells the scanf function to read in an integer. The second argument of scanf is the variable, sort of. We'll learn more about what is going on later, but the gist of it is that scanf needs to know where the variable is stored in order to change its value. Using & in front of a variable allows you to get its location and give that to scanf instead of the value of the variable. Think of it like giving someone directions to the soda aisle and letting them go get a coca-cola instead of fetching the coke for that person. The & gives the scanf function directions to the variable. 

When the program runs, each call to scanf checks its own input string to see what kinds of input to expect, and then stores the value input into the variable. 

The second printf statement also contains the same '%d'--both scanf and printf use the same format for indicating values embedded in strings. In this case, printf takes the first argument after the string, the variable this_is_a_number, and treats it as though it were of the type specified by the "format specifier". In this case, printf treats this_is_a_number as an integer based on the format specifier. 

So what does it mean to treat a number as an integer? If the user attempts to type in a decimal number, it will be truncated (that is, the decimal component of the number will be ignored) when stored in the variable. Try typing in a sequence of characters or a decimal number when you run the example program; the response will vary from input to input, but in no case is it particularly pretty. 

Of course, no matter what type you use, variables are uninteresting without the ability to modify them. Several operators used with variables include the following: *, -, +, /, =, ==, >, <. The * multiplies, the / divides, the - subtracts, and the + adds. It is of course important to realize that to modify the value of a variable inside the program it is rather important to use the equal sign. In some languages, the equal sign compares the value of the left and right values, but in C == is used for that task. The equal sign is still extremely useful. It sets the value of the variable on the left side of the equals sign equal to the value on the right side of the equals sign. The operators that perform mathematical functions should be used on the right side of an equal sign in order to assign the result to a variable on the left side. 

Here are a few examples:

a = 4 * 6; /* (Note use of comments and of semicolon) a is 24 */
a = a + 5; /* a equals the original value of a with five added to it */
a == 5     /* Does NOT assign five to a. Rather, it checks to see if a equals 5.*/ 

The other form of equal, ==, is not a way to assign a value to a variable. Rather, it checks to see if the variables are equal. It is extremely useful in many areas of C; for example, you will often use == in such constructions as conditional statements and loops. You can probably guess how < and > function. They are greater than and less than operators. 

For example:

a < 5  /* Checks to see if a is less than five */
a > 5  /* Checks to see if a is greater than five */ 
a == 5 /* Checks to see if a equals five, for good measure */ 

What is C ?

C is a computer programming language. That means that you can use C to create lists of instructions for a computer to follow. C is one of thousands of programming languages currently in use. C has been around for several decades and has won widespread acceptance because it gives programmers maximum control and efficiency. C is an easy language to learn. It is a bit more cryptic in its style than some other languages, but you get beyond that fairly quickly.

C is what is called a compiled language. This means that once you write your C program, you must run it through a C compiler to turn your program into anexecutable that the computer can run (execute). The C program is the human-readable form, while the executable that comes out of the compiler is the machine-readable and executable form. What this means is that to write and run a C program, you must have access to a C compiler. If you are using a UNIX machine (for example, if you are writing CGI scripts in C on your host's UNIX computer, or if you are a student working on a lab's UNIX machine), the C compiler is available for free. It is called either "cc" or "gcc" and is available on the command line. If you are a student, then the school will likely provide you with a compiler -- find out what the school is using and learn about it. If you are working at home on a Windows machine, you are going to need to download a free C compiler or purchase a commercial compiler. A widely used commercial compiler is Microsoft's Visual C++ environment (it compiles both C and C++ programs). Unfortunately, this program costs several hundred dollars. If you do not have hundreds of dollars to spend on a commercial compiler, then you can use one of the free compilers available on the Web. See http://delorie.com/djgpp/ as a starting point in your search.

Types of User-defined Functions in C Programming

In this tutorial, you will learn about different approaches you can take to solve a single problem using functions.

For better understanding of arguments and return value from the function, user-defined functions can be categorized as:

• Function with no arguments and no return value
• Function with no arguments and a return value
• Function with arguments and no return value
• Function with arguments and a return value.

The 4 programs below checks whether an integer entered by the user is a prime number or not. And, all these programs generate the same output.

Example #1: No arguments passed and no return Value

#include <stdio.h>

void checkPrimeNumber();

int main()
{
    checkPrimeNumber();    // no argument is passed to prime()
    return 0;
}

// return type of the function is void becuase no value is returned from the function
void checkPrimeNumber()
{
    int n, i, flag=0;

    printf("Enter a positive integer: ");
    scanf("%d",&n);

    for(i=2; i <= n/2; ++i)
    {
        if(n%i == 0)
        {
            flag = 1;
        }
    }
    if (flag == 1)
        printf("%d is not a prime number.", n);
    else
        printf("%d is a prime number.", n);
}

The empty parentheses in checkPrimeNumber(); statement inside the main() function indicates that no argument is passed to the function.

The return type of the function is void. Hence, no value is returned from the function.

The checkPrimeNumber() function takes input from the user, checks whether it is a prime number or not and displays it on the screen.

Example #2: No arguments passed but a return value

#include <stdio.h>
int getInteger();

int main()
{
    int n, i, flag = 0;

    // no argument is passed to the function
    // the value returned from the function is assigned to n
    n = getInteger();

    for(i=2; i<=n/2; ++i)
    {
        if(n%i==0){
            flag = 1;
            break;
        }
    }

    if (flag == 1)
        printf("%d is not a prime number.", n);
    else
        printf("%d is a prime number.", n);

    return 0;
}

// getInteger() function returns integer entered by the user
int getInteger()
{
    int n;

    printf("Enter a positive integer: ");
    scanf("%d",&n);

    return n;
}

The empty parentheses in n = getInteger(); statement indicates that no argument is passed to the function. And, the value returned from the function is assigned to n.

Here, the getInteger() function takes input from the user and returns it. The code to check whether a number is prime or not is inside the main() function.

Example #3: Argument passed but no return value

#include <stdio.h>
void checkPrimeAndDisplay(int n);

int main()
{
    int n;

    printf("Enter a positive integer: ");
    scanf("%d",&n);

    // n is passed to the function
    checkPrimeAndDisplay(n);

    return 0;
}

// void indicates that no value is returned from the function
void checkPrimeAndDisplay(int n)
{
    int i, flag = 0;

    for(i=2; i <= n/2; ++i)
    {
        if(n%i == 0){
            flag = 1;
            break;
        }
    }
    if(flag == 1)
        printf("%d is not a prime number.",n);
    else
        printf("%d is a prime number.", n);
}

The integer value entered by the user is passed to checkPrimeAndDisplay() function.

Here, the checkPrimeAndDisplay() function checks whether the argument passed is a prime number or not and displays the appropriate message.

Example #4: Argument passed and a return value

#include <stdio.h>
int checkPrimeNumber(int n);

int main()
{
    int n, flag;

    printf("Enter a positive integer: ");
    scanf("%d",&n);

    // n is passed to the checkPrimeNumber() function
    // the value returned from the function is assigned to flag variable
    flag = checkPrimeNumber(n);

    if(flag==1)
        printf("%d is not a prime number",n);
    else
        printf("%d is a prime number",n);

    return 0;
}

// integer is returned from the function
int checkPrimeNumber(int n)
{
    /* Integer value is returned from function checkPrimeNumber() */
    int i;

    for(i=2; i <= n/2; ++i)
    {
        if(n%i == 0)
            return 1;
    }

    return 0;
}

The input from the user is passed to checkPrimeNumber() function.

The checkPrimeNumber() function checks whether the passed argument is prime or not. If the passed argument is a prime number, the function returns 0. If the passed argument is a non-prime number, the function returns 1. The return value is assigned to flag variable.

Then, the appropriate message is displayed from the main() function.

Which approach is better?

Well, it depends on the problem you are trying to solve.  In case of this problem, the last approach is better.

A function should perform a specific task. The checkPrimeNumber() function doesn't take input from the user nor it displays the appropriate message. It only checks whether a number is prime or not, which makes code modular, easy to understand and debug.

A Short Introduction to Programming

Steve Summit

At its most basic level, programming a computer simply means telling it what to do, and this vapid-sounding definition is not even a joke. There are no other truly fundamental aspects of computer programming; everything else we talk about will simply be the details of a particular, usually artificial, mechanism for telling a computer what to do. Sometimes these mechanisms are chosen because they have been found to be convenient for programmers (people) to use; other times they have been chosen because they're easy for the computer to understand. The first hard thing about programming is to learn, become comfortable with, and accept these artificial mechanisms, whether they make ``sense'' to you or not.
In fact, you shouldn't worry if some (or even many) of the mechanisms used for programming a computer don't make sense. It doesn't make sense that the cold water faucet has to be on the right side and the hot one has to be on the left; that's just the convention we've settled on. Similarly, many computer programming mechanisms are quite arbitrary, and were chosen not because of any theoretical motivation but simply because we needed an unambiguous way to say something to a computer.

In this introduction to programming, we'll talk about several things: skills needed in programming, a simplified programming model, elements of real programming languages, computer representation of numbers, characters and strings, and compiler terminology.

Hello World Example

A C program basically consists of the following parts −

• Preprocessor Commands
• Functions
• Variables
• Statements & Expressions
• Comments

Let us look at a simple code that would print the words "Hello World" −

#include <stdio.h>

int main() {
   /* my first program in C */
   printf("Hello, World! \n");
   
   return 0;
}

Let us take a look at the various parts of the above program −

• The first line of the program #include <stdio.h> is a preprocessor command, which tells a C compiler to include stdio.h file before going to actual compilation.
• The next line int main() is the main function where the program execution begins.
• The next line /*...*/ will be ignored by the compiler and it has been put to add additional comments in the program. So such lines are called comments in the program.
• The next line printf(...) is another function available in C which causes the message "Hello, World!" to be displayed on the screen.
• The next line return 0; terminates the main() function and returns the value 0.

Compile and Execute C Program

Let us see how to save the source code in a file, and how to compile and run it. Following are the simple steps −

• Open a text editor and add the above-mentioned code.
• Save the file as hello.c
• Open a command prompt and go to the directory where you have saved the file.
• Type gcc hello.c and press enter to compile your code.
• If there are no errors in your code, the command prompt will take you to the next line and would generate a.out executable file.
• Now, type a.out to execute your program.
• You will see the output "Hello World" printed on the screen.

$ gcc hello.c
$ ./a.out
Hello, World!

Make sure the gcc compiler is in your path and that you are running it in the directory containing the source file hello.c.