Using C++11's lambda to generate desired functions with a factory.

function_generator.cpp

#include <iostream>
#include <vector>

std::function<float(float)> converter_factory(std::string region) {
    if (region == "US") {
        return [] (float celsius) -> float {
            return (celsius / 5 * 9 + 32);
        };
    }
    return [] (float fahrenheit) -> float {
        return ((fahrenheit - 32) / 9 * 5);
    };
};


int main(int argc, const char * argv[]) {    
    
    std::function<float(float)> us_converter = converter_factory("US");
    std::function<float(float)> uk_converter = converter_factory("UK");
    
    std::cout << us_converter(100) << std::endl;
    std::cout << uk_converter(100) << std::endl;
    
    return 0;
}