"Error: expected a '{' introducing a lambda body" when trying to get char from map<char,char> C++

Question

char Substitution::encodeChar(char a, std::map<char, char>&){
    return &[a];
}

This is my implementation attempt (based on a pre defined Class header which I may not change for the assignment). In Visual Studio I get the error (see title) over the semicolon?

Trying

&.find(a)

instead gives me "expected an expression" over the period.

I think I spotted somewhere saying something about const char vs. char for this problem, but I can't wrap my head around it. I've used map char char earlier this way, but somehow using it in this context doesn't work.

Answer 1

It looks like you're trying to treat & as a variable name. It's not. Variable names consist only of letters, digits, and underscores.

Actually, in the function parameters, std::map<char, char>& means that the type of the parameter is a "reference to std::map<char, char>". Note that I said "reference to". That's what the & means. It's part of the type and makes the parameter a reference parameter.

So you need to give your parameter a name and then use that name:

char Substitution::encodeChar(char a, std::map<char, char>& my_map){
    return my_map[a];
}

We can read the parameter std::map<char, char>& my_map as saying the my_map is a "reference to std::map<char, char>". Then, my_map[a] accessing the key a in that map.