factorial algorithm in pseudo code

Question

I've been given the following algorithm, that takes a positive integer K and returns a value:

X = 1
Y = 1
while X ≠ K do
    X = X + 1
    Y = Y * x
return Y

I'm supposed to figure out what it returns.

As it happens, I know the answer — it returns the factorial of K — but I don't understand why.

How do you go about figuring out what this pseudocode does?

Answer 1

Now let's assume that K is 5. Therefore the factorial of 5 is 120. Then as you enter the loop X value is 2 and y gets the value 2.(1*2) Then the value of X is 3 after getting into loop, which then makes the value of Y 6 because (3*2). Then the value of X is 4 after getting into loop, which then makes the value of Y 24 because (4*6). Then the value of X is 5 after getting into loop, which then makes the value of Y 120. Then since X==Y the while loop exits and Y value which is the factorial is returned.