Perhaps:
for k = 1:5
YourGrade= input('Enter your number grade:')
if YourGrade >= 90;
disp('Your grade is an A')
elseif YourGrade >= 80 && YourGrade < 90;
disp('Your grade is a B')
elseif YourGrade >= 70 && YourGrade < 80;
disp('Your grade is a C')
elseif YourGrade >= 60 && YourGrade < 70;
disp('Your grade is a D')
else YourGrade <= 50;
disp('Your grade is an F')
end
end
