Using an input string as a function name c++ - c++

Question

First time posting so be gentle. I've started to teach myself C++ as I've always had an interest and also it will be useful for work in the future.
Ok so i have written a very basic program that will either Add, Subtract, Multiply or Divide depending on the user input.
My question is can i use an input from the user as string and use that to call a function?
See code below:-
#include <iostream>
#include <string>
using namespace std;
// Addition Function
int Add (int a, int b)
{
int r; //Result
r=a+b; //formula
return r; //return result of formula
}
// Subtraction Function
int Subtract (int a, int b)
{
int r; //Result
r=a-b; //formula
return r; //return result of formula
}
// Multiply Function
int Multiply (int a, int b)
{
int r; //Result
r=a*b; //formula
return r; //return result of formula
}
// Divide Function
int Divide (int a, int b)
{
int r; //Result
r=a/b; //formula
return r; //return result of formula
}
// Main
int main()
{
int ip1, ip2, z;
string option;
cout << "Enter first number: ";
cin >> ip1;
cout << "Enter second number: ";
cin >> ip2;
cout << "What would you like to do?, Please type an option (Options: Add, Subtract, Multiply, Divide)\n";
getline(cin,option);
z = option (ip1,ip2);
cout << "The result is " << z;
}
So i ask the user to type in an option i.e. Add, the program then takes that string(Add) and uses it to call the Add function.
At the moment im getting a 'no match for call to '(std::string {aka std::basic_string}) (int&, int&)' error on compile
Any help would be appreciated
Thanks
Lewis

Answer 1

You can use a pretty simple if conditional tree:
if (option == "Add") z = Add(ip1, ip2);
else if (option == "Subtract") z = Subtract(ip1, ip2);
else if (option == "Multiply") z = Multiply(ip1, ip2);
else if (option == "Divide") z = Divide(ip1, ip2);
Alternatively you can use an std::map to map an std::string to the corresponding function pointer. It possibly cleaner but definitely longer to write:
std::map<std::string, std::function<int(int, int)>> mapping;
mapping["Add"] = &Add;
mapping["Subtract"] = &Subtract;
mapping["Multiply"] = &Multiply;
mapping["Divide"] = &Divide;
if (mapping.find(option) == mapping.end())
// there's no such an option
z = mapping[option](ip1, ip2);
In this particular case you can even do without std::function and just use C function pointers (for non-std::function lovers):
std::map<std::string, int(*)(int, int)> mapping;
On a side note, notice that you can get rid of a lot of lines of code and temporary variables in your function declarations:
int Add (int a, int b) { return a + b; }
int Subtract (int a, int b) { return a - b; }
int Multiply (int a, int b) { return a * b; }
int Divide (int a, int b) { return a / b; }