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

using namespace std;

int main(){

  map<const char, function<double(double,double)>> tab;

  tab.insert(make_pair('+', [](double a, double b){return a+b;}));
  tab.insert(make_pair('-', [](double a, double b){return a-b;}));

  cout << "3.5 + 4.5= " << tab['+'](3.5,4.5) << endl;
}