MATLAB: Spell cheaker stuck in loop

Question

Ive got a simple enough problem code has to make sure user input is correct but Ive made a very ugly while loop and its not working at all probably needs to be completely redone, any tips are appreciated

if true
InputString = input('Input:', 's');
lenghtInput = length(InputString);
test = 'UuGgCcAa';
i = 1;
j = 1;
c = 1;
correctInput = false;
while correctInput ~= true
  if InputString(i) ~= test(j) || j == lenghtInput
      ++j;
      ++c;
     display(i)
     if c == 3
         c = 0;
         i = i + 1;
     end
  end
  correctInput = true;
end
%code
%it needs to check the only characters used are in the test variable

Answer 1

tf = ismember(InputString, 'UuGgCcAa');
correctInput = all(tf);