Find power(n, exp) efficiently

I will discuss three approaches to find power(n, exp). power(n, exp) is defined as
power(2, 4) = 2 * 2 * 2 *2 = 16.


Iterative approach:
Space Complexity = ;
Time Complexity =
   

    result=1;
    for(i=1 ; i<=exp ; i++) {
        result *= n;
    }
    printf("Iterative method: [%d]\n", result);

Divide and Conquer / Recursive approach:

While finding power(2, 20), we know that .
i.e, .
It means that we can find solution for power(n, exp/2) and multiply that value with it again.
...
temp = power(n, exp/2);
power(n, exp) = temp * temp;
...
That is how we can avoid recomputing power(n, exp/2) TWO times.
Space Complexity = [ Used in Stack, while running the program ] ;
Time Complexity = O(log n)

int rec_pow(int n, int exp) {
    int subsoln;
    if (exp==1) {
        return n;
    }

    subsoln = rec_pow(n, exp/2);
    if (exp & 1) {
        // If exp is odd number.
        return n * subsoln * subsoln;
    }


    return subsoln * subsoln;
}

Exponentiation by Squaring / (log n) Iterative Method:
Refer: Wiki: Exponentiation by Squaring
It seems Art of Computer Programming, Volume 2: Semi numerical Algorithms by Donald Knuth ( his books are generally Juggernaut ) has discussed this method in detail. You may refer it ( I have not yet ).



This approach is implementation of the equation shown above.
Space Complexity = O(1) ;
Time Complexity = O(log n)

This code will work only for exp > 0.

    result=1;
    while(exp) {
        if (exp & 1) { // If exp is odd number.
            result *= n;
        }
        exp >>= 1;
        n *= n;
    }
    printf("Exponentiation by Squaring method: [%d]\n", result);