HQ9+ Interpreter

#include <iostream>
#include <fstream>
#include <regex>

void printLyrics() {
    for (int i = 99; i > 0; --i) {
        std::cout << i << (i == 1 ? " bottle" : " bottles") << " of beer\n";
        std::cout << "you take one down, pass it around,\n";
        std::cout << ((i - 1) == 0 ? "no more" : std::to_string(i - 1)) << " bottles of beer on the wall.\n\n";
    }
}

void processLetter(char c, const std::string& source) {
    switch (c) {
    case 'h':
        std::cout << "Hello World.\n";
        break;

    case 'q':
        std::cout << source << "\n";
        break;

    case '9':
        printLyrics();
        break;

    case '+':
#ifdef _MSC_VER
        _asm {
            inc eax
        }
#else
        __asm__("inc %eax")
#endif
        break;
    }
}

void interpret(const std::string& source) {
    std::string src = source;
    std::regex spaces("\\s+");
    std::regex_replace(src, spaces, "");

    for (auto it = src.begin(); it != src.end(); ++it) {
        char c = *it;
        processLetter(c, source);
    }
}

void runFile(const std::string& filename) {
    std::ifstream in(filename);
    std::string line;
    std::string source;

    while (std::getline(in, line)) {
        source += line;
    }

    interpret(source);
}

void runConsole() {
    while (true) {
        std::string input;

        std::cout << "> ";
        std::cin >> input;

        if (input.empty()) {
            continue;
        }

        interpret(input);
    }
}

int main(int argc, char** argv) {
    if (argc == 1) {
        runConsole();
    } else if (argc == 2) {
        runFile(argv[1]);
    }
}