Write a C program that implements the standard function char * strrchr(const char *str, int c) that returns the pointer of the last instance of the given c in string str. Return a NULL pointer if c is not found in the string. Write a C program that implements the standard function char * strstr(char *strl, char *str2) that returns the pointer of the first instance of string str2 in string strl. Return a NULL pointer if string str2 is not found in string strl