How to make a switch statement work for a matrix

I am trying to convert letters to numbers using the following switch algorithm:

switch grades
    case {'A','a'}
        GP = 4;
    case {'B','b'}
        GP = 3;
    case {'C','c'}
        GP = 2;
    case {'D','d'}
        GP = 1;
    otherwise
        GP = 0;
end

but my variable "grades" is a matrix with 16 characters and it's only returning an answer for one of the values when I run it through. How do I make it give me another matrix with the numbers for all the corresponding letters?

Answer 1

[Synthia Caruvana]

nevermind i got it fam