1. Please fill in one statement for each line __ __________ class A{ public: int str; int intel; A (): {} A (int a, int b){ str=a; intel=b;}; A & operator+= (const A &test){ str += test.str; intel += test.intel; return ; } }; int main(){ A a ,b(10,30);cout<<a+=b << a.str << a.intel << std::endl; return 0;

Actually, there is an error in the code. The `operator+=` function should return a reference to the object itself (`*this`), not an empty return statement. So the corrected code would be:

#include <iostream>

class A {
public:
    int str;
    int intel;
    A(): {}
    A(int a, int b) {
        str = a;
        intel = b;
    }
    A& operator+=(const A& test) {
        str += test.str;
        intel += test.intel;
        return *this;
    }
};

int main() {
    A a, b(10, 30);
    std::cout << (a += b).str << " " << (a += b).intel << std::endl; //test the operator
    return 0;
}

And the output would be:

20 60