Error: No match For Operator-

[1vD3vCM9]

im writing my own program, now, i wanted to do a calculator mode,
i did this:

  #include <iostream>
#include <string>
#include <windows.h>
#include "System.h"
#include "Modes.h"
#include "Dsystem.h"
#include "MyFile.h"
#include "SCalSystem.h"
#include "SCalSystem.h"

using namespace std;

SCalSystem::SCalSystem()
{
    string sum;
    string amb;
    string akb;
    string adb;
string input;
string a;
string b;
cout << "Choose First Number: \n";
cin >> a;
cout << "Choose Second Number: \n";
cin >> b;
sum = a + b;
amb = a - b;
akb = a * b;
adb = a / b;
cout << "-----------------------------------\n";
cout << a << " ? " << b << "\n";
cout << "-----------------------------------\n";
cout << "Replace The ? With:  \n\n";
cout << "1. +\n\n";
cout << "2. -\n\n";
cout << "3. *\n\n";
cout << "4. /\n\n";
cin >> input;
if(input == "1")
{
cout << "-----------------------------------\n";
cout << a << " + " << b << " = " << sum << endl;
cout << "-----------------------------------\n";
}

if(input == "2")
{
cout << "-----------------------------------\n";
cout << a << " - " << b << " = " << amb << endl;
cout << "-----------------------------------\n";
}
if(input == "3")
{
cout << "-----------------------------------\n";
cout << a << " * " << b << " = " << amb << endl;
cout << "-----------------------------------\n";
}
if(input == "4")
{
cout << "-----------------------------------\n";
cout << a << " / " << b << " = " << adb << endl;
cout << "-----------------------------------\n";
}
}

and it gives me the Error:
s Program - V.010\SCalSystem.cpp|27|error: no match for 'operator-' in 'a - b'|

[Peter87]

a and b are strings (text) so subtraction doesn't make sense. If you want to carry out arithmetic calculations on them you probably want them to be of type int or double.

[1vD3vCM9]

i see...
thank you!