Strings

A std::string knows its own length: tag.size() is the number of characters in it, and tag[0] is its first character, whose type is char. + joins two strings into one, and += adds a character or a string to the end. substr(start, count) cuts out part of a string, so if tag is "layan#1024", then tag.substr(0, 5) is "layan". tag.find('#') returns the position where the character first appears, and if it isn't there, it returns a special value called std::string::npos, which is neither -1 nor zero, so compare against it explicitly.

Note that + needs at least one of its two sides to be a std::string. The compiler accepts "HP: " + 2, but it doesn't join anything: it skips the first two characters of the text and prints ": ". So convert the number to a string first: "HP: " + std::to_string(hp).

std::toupper(c) and std::tolower(c) from <cctype> convert a single unaccented letter, A to Z, to upper or lower case, and they return an int, so turn the result back into a character with static_cast<char>. Also keep in mind that std::string stores bytes, not characters, and an accented letter like é takes two bytes in UTF-8, so std::string("José").size() is 5, and [3] is only half of the é. That's why the player names in this lesson's examples use plain unaccented letters: handling text like José one character at a time needs different tools.