+= operator overloading a struct

Overloading the shorthand addition operator (+=) in c++: Note, this is operator overloading the += operator for a STRUCT. called "deathNote". I follow the constant-class rule for classes. But use lowercase for structs because structs are value-types / primitives. So they should be treated like "int", "float", "char", "string", etc. Which all start with lowercase letters.

deathNote operator_-(const deathNote &a){
    this->apples = a.apples + this->apples;
    this->chocolate = a.chocolate + this->chocolate;
    this->paper = a.paper + this->paper;
    return (*this);
}