How to make efficient C++ jump table?

Question

I'm beginner to C++ and I have implemented the following simple jump table, but was wondering if I'm doing it the right way. Is there anyway I can improve the following code?

The following code is using a dictionary (I'm from a C# background) to store functions' pointers.

#include <cstdio>
#include <iostream>
#include <string>
#include <unordered_map>

using namespace std;

void Zero() { printf("Zero\n"); }
void One() { printf("One\n"); }   
void Two() { printf("Two\n"); }
void Three() { printf("Three\n"); }

string prompt()
{
    printf("Enter number from 0 to 3 or q to quit:\n");
    string line;
    getline(cin, line);

    return line;
}

int main(int argc, const char * argv[]) {

    unordered_map<string, void(*)()> map;

    map["0"] = Zero;
    map["1"] = One;
    map["2"] = Two;
    map["3"] = Three;

    while (true) {
        string c = prompt();
        if (c == "q") break;

        map[c]();
    }
    return 0;
}

Answer 1

How about a switch statement?

switch (c) {
   case 0:
      printf("Zero\n"); break;
   case 1:
      printf("One\n"); break;
   case 2:
      printf("Two\n"); break;
   case 3:
      printf("Three\n"); break;
   default:
      break;
}

Answer 2

There's not much you can do to make your code "faster" without going for the switch solution which breaks the original idea of having an array of functions. If you only gonna use 'characters' such as '0' => '9', 'a' => 'z' you could dodge the memory allocation needed for the string, and you could also initialize your map with an initializer_list, and you could also make such array const static if that's viable.

Here goes my "optimized" code if it helps.

inline char prompt() //this function will probably 900% be inlined even if you don't specify the inlike keyword
{
    printf("Enter number from 0 to 3 or q to quit:\n");
    char v;
    while (!(std::cin >> v)); //Just to make sure we get valid input
    return v;
}

int main()
{
    static const std::unordered_map<char, void(*)()> mymap = 
    {
        { '0' , Zero },
        { '1' , One },
        { '2' , Two },
        { '3' , Three }
    };

    while(1)
    {
        auto it = mymap.find(prompt());

        // Without this check, your program will crash if input is invalid.
        if (it != mymap.end()) 
        {
            it->second();
            break;
        }
    }

    return 0;
}