Write a program with three functions: upper, lower, and reverse. The upper function should accept a pointer to a C-string as an argument. It should step through each character in the string, converting them to uppercase. The lower function, too, should accept a pointer to a C-string as an argument. It should step through each character in the string, converting it to a lowercase. Like upper and lower, reverse should also accept a pointer to a string. As it steps through the string, it should text each character to determine whether it is uppercase or lowercase. If the character is upper case, it should be converted to lowercase. Likewise, if a character is lowercase, it should be converted to uppercase.