Problem B: Change Letter Case (20 points) Your solution cannot use any built-in C + functions. Refer to the ASCII chart on the C++ reference sheet or google for an ASCII chart. Make a program that asks a user to enter a letter (a character). If the character is a lowercase letter, the program converts it to uppercase. If the letter is an uppercase letter the program converts it to lowercase. Do this only if the entered character is part of the alphabet (i.e. a-z or A-Z). Example 1 (user input is underlined for clarity, underlined text in your program is not needed): Enter a letter: d The uppercase of d is D. Example 2 (user input is underlined for clarity, underlined text in your program is not needed): Enter a letter: Example 3 (user input is underlined for clarity, underlined text in your program is not needed): Enter a letter: 44 is not a letter! Test your program using not only the example data above, but other cases as well. And revise your program until you are sure it is correct