What is Libraries file in C

Another component common to C programs is the header file. This supplies information about the standard library functions. These files all end with the .h extension and are added to the program using the #include pre-processor directive. All C compilers use a pre-processor as their first phase of compilation to manipulate the code of the source file before it is compiled.

Pre-processor directives are not actually part of the C language, but rather instructions from you to the compiler. The #include directive tells the pre-processor you want to read another file and include it with your program.

The most commonly required header file is stdio.h. The directive to include this file is:
#include <stdio.h>

The filename can be in upper or lower case, but lower case is the norm. The stdio.h header file contains, among other things, information related to the printf() function. Notice that the #include directive does not end with a semi-colon. This is because #include is not a keyword that can define a statement, it is an instruction to the compiler.

With few exceptions, C ignores spaces. Having said that spaces and indentation are very important when it comes to reading and debugging the code.

Example 1:

Since all C programs share common elements, understanding one program will help you understand many others. One of the simplest programs is:

#include <stdio.h> 
int main(void) 
{ 
        printf("My first program in C.");     
    return 0; 
 } 

The fourth line:

printf(“This is a short C program.”):
The printf() function outputs the characters that are contained between the quotes to the screen. printf() is a standard library function which displays the string on the screen.

Input from the keyboard:

scanf() is a standard library function to read a value such as an integer or string from the keyboard.

Example 2: 
#include <stdio.h> 
int main(void) 
{     
    int Number; 
        printf("Enter a Number");     
    scanf("%d", &Number);     getch();     
    return 0; 
} 
Lines 3 (int Number) will be examined in a further lesson. 
The seventh line: getch();

The function named getch() is a get character function that reads the character in from the keyboard, and puts it directly into the program where it is operated on immediately. This program therefore reads a character and immediately displays it on the screen. Notice the use of the keyword void in between the brackets – this signals no vales are being passed to the function main when execution of the function begins – use this from now on.