It is good programming style to always use a for loop when the number of times to repeat the action is known. The following code uses a while loop that mimics what a for loop should do. Rewrite it using a for loop that accomplishes exactly the same thing.
myprod = 1;
i = 1;
while i <= 4
num = input('Enter a number: ');
myprod = myprod ⁎ num;
i = i + 1;
end