1. struct BadLengthException{ int n; BadLengthException(int n){ this->n = n; } int what(){ return n; } };

C++14 per API that derives from std::exception instead of a free-floating class/struct.

class BadLengthException : exception {
public:
    BadLengthException( int length ) : message_(to_string(length)) {}
    const char* what() const noexcept override { return message_.c_str(); }
private:
    string message_;
};

I kept it as a struct, since that is what was provided. For those that may not already know, a struct is essentially the same as a class - only that it is 'public' by default, opposed to classes which are 'private' by default.

solution

struct BadLengthException{
    int n;
    BadLengthException(int n){
        this->n = n;
    }
    int what(){
        return n;
    }
};

class BadLengthException { int n=0; public: BadLengthException(int x){ n+=x; } int what(){ return n; } };

As part of a Tech Base website I'm creating tool-based websites like mouse tests using C++. Can anyone help me or guide me through this process?