error: no match for 'operator-' When trying to subtract strings

Question

I am trying to subtract these two numbers, and I keep getting this error.

code:

#include <iostream>

using namespace std;


void Cal()
{
string Money = "back";
string TotPay = "back";
string Assets = "back";
cout << "At anytime, you can type the word 'back' to go back a step." << endl;
do{
    cout << "Enter your total amount of money: ";
    cin >> Money;
}while(Money == "back");
do{
    cout << "\nEnter the total of your payments: ";
    cin >> TotPay;
}while(TotPay == "back");
do{
    cout << "\nEnter the total value of your assets: ";
    cin >> Assets;
}while(Assets == "back");
cout << "Your net worth is " << (Money + Assets) - TotPay << "!";

}

int main()
{
string name;
string yn;
cout << "Enter your name please: ";
cin >> name;
cout << "\nHello " << name << ", today we are going to calculate your net worth.\n";
do{
    Cal();
    cout << "Would you like to calculate again? (yes/no)\n";
    cin >> yn;
}while(yn == "yes");
cout << "See ya!";
return 0;

}

The error is on the line of code that says

cout << "Your net worth is " << (Money + Assets) - TotPay << "!";

The program will not ever compile with the subtraction sign (-) there, and if I change it to a addition sign (+) then it will compile, but the numbers will not properly add, and the end number just ends up being a place holder number for the variable (for example, 2555354 or something like that). Am I missing something here? Any help would be appreciated.

Answer 1

You are trying to add and subtract strings, not numbers. While addition works (and results in string concatenation), subtracting strhings doesn't make sense. Use numbers:

int Money = 0;
int TotPay = 0;
int Assets = 0;

Depending on your applications need, you might want to use a different numeric type, eg double .

Answer 2

Although others have pointed out rightly..

To get this code working, the string values need to be treated as an integer:

cout << "Your net worth is " << (stoi(Money) + stoi(Assets)) - stoi(TotPay) << "!";