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 it 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 lowercase. Like upper and lower, reverse should also accept a pointer to a string. As it steps through the string, it should test each character to determine whether it is upper- or lowercase. If a character is uppercase, it should be converted to lowercase. Likewise, if a character is lowercase, it should be converted to uppercase. Test the functions by asking for a string in function main, then passing it to them in the following order: reverse, lower, and upper.