Writing the First C Program

WRITING THE FIRST C PROGRAM

To write a C program, we first need to write the code. For this, open a text editor. If you are a Windows user you may use Notepad and if you prefer working on UNIX/Linux you can use emacs or vi. Once the text editor is opened on your screen, type the following statements:

#include <stdio.h>

int main()

{

printf("\n Welcome to the world of C");

return 0;

}

Output

Welcome to the world of C

#include <stdio.h>

This is a preprocessor command that comes as the first statement in our code. All preprocessor commands start with symbol hash (#). The #include statement tells the compiler to include the standard input/output library or header file (stdio.h) in the program. This file has some in-built functions. By simply including this file in our code we can use these functions directly. The standard input/ output header file contains functions for input and output of data like reading values from the keyboard and printing the results on the screen.

int main()

Every C program contains a main() function which is the starting point of the program. int is the return value of the main() function. After all the statements in the program have been written, the last statement of the program will return an integer value to the operating system. The concepts will be clear to us when we read the chapter on Functions. So even if you do not understand certain things, do not worry.

Programming Tip: If you do not place a parenthesis after 'main', a compiler error will be generated.

{} The two curly brackets are used to group all the related statements of the main function. All the statements between the braces form the function body. The function body contains a set of instructions to perform the given task.

 printf("\n Welcome to the world of C ");

The printf function is defined in the stdio.h file and is used to print text on the screen. The message that has to be displayed on the screen is enclosed within double quotes and put inside brackets.

Programming Tip: Placing a semi- colon after the parenthesis of main function will generate a compiler error.

The message is quoted because in C a text (also known as a string or a sequence of characters) is always put between inverted commas. '\n' is an escape sequence and represents a newline character. It is used to print the message on a new line on the screen. Like the newline character, the other escape sequences supported by C language are shown in Table 2.1.

Note                                                         

Escape sequences are actually non-printing control characters that begin with a backslash (\).

return 0;

This is a return command that is used to return the value 0 to the operating system to give an indication that there were no errors during the execution of the program.

Note

Every statement in the main function ends with a semi- colon (;).

Now that you have written all the statements using the text editor, save the text file as first.c. If you are a Windows user then open the command prompt by clicking Start->Run and typing 'command' and clicking Ok. Using the command prompt, change to the directory in which you had saved your file and then type:

C:\>tc first.c

In case you are working on UNIX/Linux operating system, then exit the text editor and type

$cc first.c -ofirst

The -o is for the output file name. If you leave out the -o then the file name a.out is used.

This command is used to compile your C program. If there are any mistakes in the program then the compiler will tell you the mistake you have made and on which line you made it. In case of errors you need to re-open your .c file and correct those mistakes. However, if everything is right then no error(s) will be reported and the compiler will create an . exe file for your program. This .exe file can be directly run by typing

'hello.exe' for Windows and ‘./hello' for UNIX/Linux operating system.

When you run the .exe file, the output of the program will be displayed on screen. That is,

Welcome to the world of C

Note

The printf and return statements have been indented or moved away from the left side. This is done to make the code more readable.