C++ toplama çıkarma islemi

#include <iostream>
using namespace std;
int main ()
{
int a,b;
string c;
cout <<"Enter the operation type (+ or -): "; cin >> c;
cout << "Enter the numbers: "; cin >> a >>b;
if (a==0 || b==0)
{
cout <<"Operation can not be done";
}
else if (c=="+" || c=="-")
{
if (c=="+")
{
double r;
r=(1/a)+(1/b);
cout <<"******\n";
cout <<"1/" << a << "+" <<"1/" << b << "=" << r << endl;
}
else
{
double r;
r=(1/a)-(1/b);
cout <<"******\n";
cout <<"1/" << a << "-" <<"1/" << b << "=" << r << endl;
}

}
else
{
cout <<"Invalid operation";
}
}

#include <iostream>
using namespace std;
int main()
{
    int a, b;
    string c;
    cout << "Enter the operation type (+ or -): "; cin >> c;
    cout << "Enter the numbers: "; cin >> a >> b;
    if (a == 0 || b == 0)
    {
        cout << "Operation can not be done";
    }
    else if (c == "+" || c == "-")
    {
        if (c == "+")
        {
            int r;
            r = a + b;
            cout << "**\n";
            cout << "result : " << a << " + " << b << " = "  << r;
        }
        else
        {
            int r;
            r = a - b;
            cout << "**\n";
            cout << "result : " << a << " + " << b << " = " << r;
        }

    }
    else
    {
        cout << "Invalid operation";
    }
}