good_input = 0;
while (not good_input) {
    display menu
    get user input
    if user input == 1
        do stuff for choice one
        set good_input true
    elsif user input == 2
        do stuff for choice two
        set good_input true
    # continue processing choices with elsif,
    # but the last bit should be the default
    # case:
    else
        display error message
}