Power of Two - Implementation

Here's the complete solution:

function isPowerOfTwo(n)
    if n ≤ 0 then
        return false
    while n > 1
        if n mod 2 ≠ 0 then
            return false
        n := n / 2
    return true

Each division by $2$ reduces $n$. If at any point $n$ is odd (modulo $2 \neq 0$), you know it's not a power of two. The loop runs at most $\log_2(n)$ times.