mul.cpp

#include <iostream>

struct longNumber {
	int length;
	unsigned char *digits;
};

longNumber multiply(longNumber a, longNumber b) {
	longNumber result;
	result.length = a.length + b.length;
	result.digits = new unsigned char[result.length];
	return result;
}

void checkMultiplication(longNumber a, longNumber b, longNumber expectedResult) {
	longNumber actualResult = multiply(a, b);
	if (actualResult.length != expectedResult.length) {
		std::cout << "Wrong multiplication result: length mismatch" << std::endl;
		return;
	}

	for (int i = 0; i < actualResult.length; i++) {
		if (actualResult.digits[i] != expectedResult.digits[i]) {
			std::cout << "Wrong multiplication result: digit mismatch" << std::endl;
			return;
		}
	}

	std::cout << "Correct multiplication result" << std::endl;
}

int main() {
	longNumber one;
	one.length = 1;
	one.digits = new unsigned char[one.length];
	one.digits[0] = 1;

	longNumber one2byte; // = {2, {0, 1}};
	one2byte.length = 2;
	one2byte.digits = new unsigned char[one2byte.length];
	one2byte.digits[0] = 0;
	one2byte.digits[1] = 1;

	checkMultiplication(one, one, one2byte); // one * one == one2byte
}