What's wrong with my program

#include<iostream>

using namespace std;
class calc
{
    int a,b,c;
public:
    void add()
    {
        cout<<"Enter values";
        cin>>a>>b;
        c=a+b;
        cout<<c;
    }
    void mul()
    {
        cout<<"enter values";
        cin>>a>>b;
        c=a*b;
        cout<<c;
    }
};
int main()
{
    calc obj;
    char f[10];
    cout<<"Select from the option 1. add, 2. mul";
    cin>>f;
    if(f=="add")
        obj.add();
    else if(f=="mul")
        obj.mul();
    else
        cout<<"invalid choice";

        return(0);

}