//Multiply two strings representing decimal values
std::string decimalMul(std::string a, std::string b) {
std::string o = "0";
for (unsigned i = 0; i < b.length(); i++) {
std::string n = decimalDigitMul(a, b[i] - '0');
if (n != "0") {
for (unsigned j = i + 1; j < b.length(); j++) n += "0";
}
o = decimalAdd(o, n);
}
return o;
}
//Helper function for decimalMul
std::string decimalDigitMul(std::string a, int dig) {
if (dig == 0) return "0";
else return decimalAdd(a, decimalDigitMul(a, dig - 1));
}
//Helper function for decimalMul
static std::string decimalDigitMul(const std::string &a, int dig) {
if (dig == 0) return "0";
else return decimalAdd(a, decimalDigitMul(a, dig - 1));
}
