I$\text{'}$m trying to make a lower case letter to an upper case letter in C$++.$ I need to use the toupper function. I have a list of choices: $($A$,$ B$,$ C$,$ or D$)$ and the if the user inputs $"$a$"$ I need the program to understand they mean choice $"$A$"$ so they can get the correct result because right now when I input $"$a$"$ I get "invalid" but if I input $"$A$"$ I get my correct result.