Some important header files in C

1. <stdio.h>:
 input and output function in program.
2. <conio.h>:
 to clear screen and pause information function.
3. <ctype.h>: 
function for testing characters
4. <string.h>: 
function for manipulating string
5. <math.h>: mathmatical function
6. <stdlib.h>:
 utility function for number, conversion, storage allocation
7. <assert.h>: 
function that can be used to add diagnostics to a program
8. <stdarg.h>: 
function that can be used to step through a list of function arguments
9. <setjmp.h>:
 function that can be used to avoid the normal call and return sequence
10. <signal.h>: 
function for handling exceptional condition that may arise in a program
11. <time.h>: 
function for manipulating date and time
12. <limits.h>: 
constant definitions for the size of C data types
13. <float.h>:
 definitions relating to floating-point arithmetic