Why is this string operation not working? - c++

Question

Here is the code:
#include <cmath>
#include <iostream>
using namespace std;
int main()
{
string sidelength;
cout << "Perimeter of Square" << endl;
cout << "Enter length of one side: ";
getline(cin, sidelength);
cout << sidelength * 4 << endl;
return 0;
}
When run, this is the error message:
error: no match for 'operator*' (operand types are 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' and 'int')|
How do I fix this error and make the program run correctly?

Answer 1

The get line function takes a string as it's second parameter, but you want to get an integer/double/float as an input. So don't use getline. Simply run this code below and it will solve your problem.
#include <cmath>
#include <iostream>
using namespace std;
int main()
{
int sidelength;
cout << "Perimeter of Square" << endl;
cout << "Enter length of one side: ";
cin >> sidelength;
cout << sidelength * 4 << endl;
return 0;
}

Answer 2

If you really want to multiply a string by a number, you can overload operator*:
#include <cmath>
#include <iostream>
#include <cctype>
#include <string>
std::string operator*(const std::string &s,int x) {
std::string result;
try {
result = std::to_string(stoi(s)*x);
} catch(const std::invalid_argument&) {
result="UND";
}
return result;
}
std::string operator*(const std::string &s,double x) {
std::string result;
try {
result = std::to_string(stof(s)*x);
} catch(const std::invalid_argument&) {
result="UND";
}
return result;
}
int main()
{
std::string input("1");
input = input * 5.32;
std::cout << input << std::endl;
input = input * 2;
std::cout << input << std::endl;
return 0;
}