leetcode complex number multiplication

class Solution {
public:
    string complexNumberMultiply(string a, string b) {
        int ra, ia, rb, ib;
        char buff;
        stringstream aa(a), bb(b), ans;
        aa >> ra >> buff >> ia >> buff;
        bb >> rb >> buff >> ib >> buff;
        ans << ra*rb - ia*ib << "+" << ra*ib + rb*ia << "i";
        return ans.str();
    }
};
or
string complexNumberMultiply(string a, string b) {
    int a1 = 0, b1 = 0, a2 = 0, b2 = 0;
    sscanf(a.c_str(), "%d+%di",&a1,&b1);
    sscanf(b.c_str(), "%d+%di",&a2,&b2);
    return to_string(a1*a2-b1*b2)+"+"+to_string(a1*b2+a2*b1)+"i";
}