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
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 beused 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
7. <assert.h>: function that can beused 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