ex14.44.cpp

/***************************************************************************
 *  @file       main.cpp
 *  @author     Alan.W
 *  @date       21  Jan 2014
 *  @remark     This code is for the exercises from C++ Primer 5th Edition
 *  @note
 ***************************************************************************/
//!
//! Exercise 14.44:
//! Write your own version of a simple desk calculator that can handle binary operations.
//!

#include <iostream>
#include <string>
#include <map>
#include <functional>

//! normal function
int add(int i, int j)
{
    return i + j;
}

//! named lambda
auto mod = [] (int i, int j)
{
    return i % j ;
};

//! functor
struct wy_div
{
    int operator ()(int denominator, int divisor)
    {
        return denominator / divisor ;
    }
};


//! the map
std::map<std::string, std::function<int(int, int)>>  binops =
{
    {"+", add},                                 //  function pointer
    {"-", std::minus<int>()},                   //  library functor
    {"/", wy_div()},                            //  user-defined functor
    {"*", [] (int i, int j) { return i*j; }},   //  unnamed lambda
    {"%", mod}                                  //  named lambda object
};


int main()
{
    while(true)
    {
        std::cout << "\npleasr enter: num operator num :\n";
        int n1 , n2;    std::string s;
        std::cin >> n1 >> s >> n2;

        std::cout << binops[s] (n1, n2);
    }

    return 0;
}