What are the functions of the following header files:
(i) ctype.h
(ii) string.h 

Ans:
(i) ctype.h: It is a header file that contains character testing and conversion functions.
For example isalpha (c) returns an int type data and determine if the argument c is
alphabetic. It returns nonzero value if true; 0 otherwise.
toascii(c ): is a conversion function defined in ctype.h that converts value of
argument to ascii.
(ii) string.h: It is also a standard header file that contains string manipulation funcions.
For example strcmp(c1,c2) function compares two strings c1 and c2
lexicographically. It returns a negative value if c1<c2; 0 if c1 and c2 are identical;
and a positive value if c1>c2.