In the C language

A. Develop change case () Function Write a function that accepts a char input variable cIn and returns a char value according to the following: 1. If the input value is a lower-case letter (a, b, ..., z), return the corresponding upper-case value. If the input value is an upper-case letter (A, B, .. . , Z), return the corresponding lower-case value If the input value is not a letter, print the message "THAT IS NOT A LETTER!" and return the input value unchanged. a. b. c. Use ihe followint; function protoiyx: char change_case (char cln) Use the main program "main - change_case.c" to test your function change_case). It uses a do-while loop that allows the user to continuously enter one character and test the function. It incorporates prompting of the user and prints messages. When the user enters the ESC key the program exits 2