#include <stdio.h>

int multiplication(int num1, int num2);
int multiplication_loop(int num1, int num2, int tmp);

// Multiplication function
int multiplication(int num1, int num2) {
	return multiplication_loop(num1, num2, 0);
}

// recursive function that calculate multiplication
// The tmp variable's value is the count of bit of num2 currently being calculated.
int multiplication_loop(int num1, int num2, int tmp) {
	// Integer is 32bit.
	if(tmp == 32)
		return 0;
	// if current bit of num2 is 1, add the value that shifts num1 variable and tmp variable.
	return ((num2 & 1) ?  num1 << tmp : 0) + multiplication_loop(num1, num2 >> 1, tmp + 1);
}

int main() {
	printf("%d", multiplication(10, 5));
	return 0;
}