Main.cpp

void encodeVignère(std::tstring& input, const std::tstring& key) {
    std::function<bool (std::tstring::value_type)> predicate =
        [](std::tstring::value_type value)
        {
            return !((value >= 'A' && value <= 'Z') || (value >= 'a' && value <= 'z'));
        };

    std::tstring::iterator invalidChar = std::find_if(input.begin(), input.end(), predicate);
    if(invalidChar != input.end())
        throw std::exception("Invalid input provided!");

    std::tstring::const_iterator invalidKey = std::find_if(key.begin(), key.end(), predicate);
    if(invalidKey != key.end())
        throw std::exception("Invalid key provided!");

    uint32 keyIndex = 0;
    for(std::tstring::reference ref : input) {
        std::tstring::const_reference keyChar = key[(keyIndex++) % key.length()];
        uint32 keyOffset = 0;
        if(keyChar >= 'A' && keyChar <= 'Z')
            keyOffset = (uint32)(keyChar - 'A');
        else
            keyOffset = (uint32)(keyChar - 'z');

        bool isUpperCase = (ref >= 'A' && ref <= 'Z');
        std::tstring::value_type maxChar = isUpperCase ? 'Z' : 'z';
        std::tstring::value_type minChar = isUpperCase ? 'A' : 'a';

        uint32 newKey = (uint32)ref + keyOffset;
        newKey -= minChar;
        newKey %= 26;
        newKey += minChar;

        ref = (std::tstring::value_type)newKey;
    }
}

void decodeVignère(std::tstring& input, const std::tstring& key) {
    std::function<bool (std::tstring::value_type)> predicate =
        [](std::tstring::value_type value)
        {
            return !((value >= 'A' && value <= 'Z') || (value >= 'a' && value <= 'z'));
        };

    std::tstring::iterator invalidChar = std::find_if(input.begin(), input.end(), predicate);
    if(invalidChar != input.end())
        throw std::exception("Invalid input provided!");

    std::tstring::const_iterator invalidKey = std::find_if(key.begin(), key.end(), predicate);
    if(invalidKey != key.end())
        throw std::exception("Invalid key provided!");

    uint32 keyIndex = 0;
    for(std::tstring::reference ref : input) {
        std::tstring::const_reference keyChar = key[(keyIndex++) % key.length()];
        uint32 keyOffset = 0;
        if(keyChar >= 'A' && keyChar <= 'Z')
            keyOffset = (uint32)(keyChar - 'A');
        else
            keyOffset = (uint32)(keyChar - 'z');

        bool isUpperCase = (ref >= 'A' && ref <= 'Z');
        std::tstring::value_type maxChar = isUpperCase ? 'Z' : 'z';
        std::tstring::value_type minChar = isUpperCase ? 'A' : 'a';

        int32 newKey = (int32)ref - keyOffset;
        newKey -= minChar;
        if(newKey < 0)
            newKey = 26 + newKey;

        newKey += minChar;

        ref = (std::tstring::value_type)newKey;
    }
}