How to write a function/procedure that multiply 2 natural numbers without * operator?

Question

So I was given a computer science problem to write a function which accepts two natural numbers and returns their product. The rules are that I am only allowed to use the addition of 1 (variable + 1), assigning and comparison operation. I end up with this code in python:

def multiplication_of_ab(a, b):
    placeholder = 0
    result = 0
    for counter in range(b):
        while (placeholder < a):
            placeholder += 1
        result += placeholder
        placeholder = 0
    return result

if __name__ == "__main__":
    print(mulitplication_of_ab(3, 4))

Maybe there is a solution that better fills the conditions?

Answer 1

Since it says "only comparisons", I assume that range is not allowed - fortunately, you can do the same thing with a while loop. (I guess while loops are allowed...) So, this code:

for i in range(5):
    print(i)

Can be re-written as:

i = 0
while i < 5:
    print(i)
    i += 1

So here is the multiply function:

def multiply(a, b):
    answer = 0
    i = 0
    # loop `a` times
    while i < a:
        j = 0
        # loop `b` times
        while j < b:
            # this line gets run `a * b` times
            answer += 1
            j += 1
        i += 1
    return answer