Multiple Input Range Sum

#include <iostream>
int main() {
    int v1 = 0, v2 = 0, sum = 0;
    std::cout << "Enter two numbers: " << std::endl;
    std::cin >> v1 >> v2;
    if (sum = 0) {
        while (v1 < v2)
            sum += v1;
            ++v1;
    } else {
        while (v1 > v2)
            sum -= v1;
            --v2;
    }
    std::cout << "Sum is: " << sum << std::endl;
    return 0;
}