sample.c

//
// Code fragment based on http://stackoverflow.com/q/11515064/827263
//

int main()
{   

    cout << "Do you want to add, subtract, multiply or divide? I want to : " << endl;
    cin >> ans;

    if (ans == "add") {
        OperateClass opOper;
        opOper.add();

    }   
    else if (ans == "subtract") {
        OperateClass opOper
        opOper.subtract();
    }   
    else if (ans == "multiply") {
        OperateClass opOper
        opOper.multiply();
    }   
    else if (ans == "divide") {
        OperateClass opOper
        opOper.divide();
    }   
}