[ale] C++ "not all control paths return a value"

[jloden at toughguy.net (Jay Loden)]

I've got some code that compiles, but with a warning for the following 
function:

string truncPath(string name){
    if(name.substr(1, 1) == ":"){
        for(int k=0; k < 30; k++){
            if(name.substr(name.length()-k, 1) == "\\"){
                string ret = name.substr(name.length()-k+1, k);
                return ret;
            }
        }
    }

    else{
        return name;
    }
}

Saying "Not all control paths return a value" - what does this mean, am 
I missing something in my code?

-Jay