Tutorial Online: First C Program Hello World

Wednesday, February 18, 2015

First C Program Hello World

We have gained lots of theoretical knowledge. Now its time to move on and write our first C program and understand it.

Hello World C Program

This is a program to print “Hello World”

#include<stdio.h>

void main()
{
 printf("Hello World");
}

Output

Hello World

Now try to understand this program step by step.

1. #include<stdio.h>: First statement started with #, it is called pre-processor directive. We will learn about them thoroughly in later tutorials. #include<stdio.h> is used to include the stdio.h header file in our program. Header files contains the functions that we use in our program. Here we have used printf() function which is present in stdio.h header file.

2. void main(): Here main() is the function. A program always starts with the main() function and every program must have main(). Here void is the return type of this function. It means main() function will not return anything. The opening curly braces ({) and closing curly braces (}) shows the body of the function.

main() can also be called as a collection of statements.

3. printf(): Here printf() is another function. This is used to print the values on the screen. Its general form is

printf(“Statement you want to print on screen”);

4. Semicolon (;) is used for denoting the termination of statement. It is also called statement terminator in C Language.

How to compile and execute?

Here we are using TURBO C compiler. If you have not downloaded it yet than download it from here.

1. Open Turbo C and type the program.
2. After that press F2 to save the program with .c extension. Eg: program.c
3. Now Press ALT + F9 to compile and CTRL + F9 to run the program.
4. Press ALT + F5 to view the output.

Well this is the easiest C program. Now lets move on and try slightly complicated program of multiplication of two numbers.

C Program to multiply two numbers

#include<stdio.h>

void main()
{
 int a, b, c;
 a=3;
 b=4;
 c=a*b;
 printf("Answer is %d",c);
}

Output

Answer is 12

Now lets try to understand this program.

1. First two statements are same as above program. In the third statement I have written

int a, b, c;

Here int is the keyword for integer and a, b and c are the integer variables. So they can only store integer values.

2. In the next two statements I have written

a=3;
b=4;

In these statements we are storing the values 3 and 4 in a and b variables respectively.

3. In the next statement

c=a*b;

We are multiplying the values in a and b, and storing them in the variable c.

4. Now in the last statement we are printing the value which is in c. A new thing %d which we have used in this program. It is called format specifier. It usually tell the compiler that it has to print the integer value on screen which is present in a variable.

Some common format specifiers are given below

a. %d for integers
b. %c for characters
c. %f for floating point numbers or real numbers

A bit elaborated form of printf() is given below

printf(“string you want to print ”, variable);

Suppose we have to print the value in b so we will use the function.

printf(“%d”,b);

Things to keep in mind

1. Use semicolon at the end of each statement.
2. Type the statements in main program as the way you want them to be executed.
3. Never try to memorise any program. Just try to understand it.
4. Learning programming is all about practical. So start doing practical from now.

Tutorial Online