% Initialize data:
clc, clear       % setup MATLAB
STOP = -1;       % stopping value for grade entry
maxGrade = STOP; % max grade so far
grade = input('Enter a grade: '); % current grade so far

% Find max grade from user input until out-of-bounds
% value is entered:
while grade >= 0 && grade <= 100
   
   % Update max grade if current grade is bigger:
   if grade > maxGrade
       maxGrade = grade;
   end
   
   % Get next grade to process:
   grade=input('Enter a grade: ');
end

% Report results:
if maxGrade == STOP
    disp('nothing valid was entered')
else
    disp(['Max grade: ',num2str(maxGrade)])
end