tolower()

  #include <ctype.h>

  

  int tolower(int ch);

  

tolower() converts any upper-case character in the range from A to Z into a lower-case character from a to z.

If ch is an upper-case character, the corresponding lower-case letter. Otherwise, ch is returned (unchanged).

isalnum(), isalpha(), iscntrl(), isdigit(), isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(), and isxdigit(),

toupper()