Why we need to use # include < math.h >, # include < ctype.h >, # include < stdio.h >, # include < conio.h >, # include < stdlib.h > and # include < string.h >.

Ans: # include < math.h > :- For using some mathematical function we need this header file. Some of the important mathematical functions in header file math.h are:- sin(), cos(), sqrt() etc.

# include < ctype.h >: All the character functions require ctype.h header file. The following lists are some function of ctype.

islower(c)            It returns True if C is a lowercase letter otherwise False.

isupper(c)           It returns True if C is an uppercase letter otherwise False.

Etc.

# include < stdio.h >: Standard input output. The following are the list of functions are in stdio.h

                                gets()    It gets a string terminated by a newline character from the standard input stream stdin.

puts()    It takes a string which is to be sent to output device.

Etc.

# include < conio.h >:  Console Input Output. The following are the list of functions are in conio.h

                                clrscr()  It clears the output screen.

                                getch() Gets a character from the console but does not echo in the screen.

Etc.

# include < stdlib.h>: General purpose standard library functions. The following are the list of functions are in stdlib.h

randomize()       It initializes / seeds the random number generator with a random number

random(n)          It generates a random number between o to n-1

Etc.

# include < string.h >: String Functions. The string functions are present in the string.h header file. Some string functions are given below:

strlen(S)               It gives the no. of characters including spaces present in a string S.

strcat(S1, S2)      It concatenates the string S2 onto the end of the string S1. The string S1 must have enough locations to hold S2.

strcpy(S1, S2)     It copies character string S2 to string S1. The S1 must have enough storage locations to hold S2.

Etc.