大佬们，主函数中t3=t1+t2;为什么错了？

Question

#include<iostream>
using namespace std;
class Complex {
private:
	double real;
	double imag;
public:
	Complex();
	Complex(double a, double b);
	Complex operator + (Complex& t1);
	friend istream& operator >>(istream&, Complex&);
	friend ostream& operator <<(ostream&, Complex&);
	Complex operator=(Complex& t);


};
Complex::Complex() {
	real = 0;
	imag = 0;
}
Complex::Complex(double a, double b) {
	real = a;
	imag = b;
}
Complex Complex::operator+(Complex& t1) {
	Complex t;
	t.real = this->real + t1.real;
	t.imag = this->real + t1.imag;
	return t;
}
Complex Complex::operator=(Complex& t) {
	Complex t1;
	t1.real = t.real;
	t1.imag = t.imag;
	return t1;
}
ostream& operator<<(ostream& output, Complex& t) {
	output << "(" << t.real << "+" << t.imag << "i)" << endl;
	return output;
}
istream& operator>>(istream& input, Complex& t) {
	cout << "请输入2个数：" << endl;
	input >> t.real >> t.imag;
	return input;
}

int main() {
	Complex t1, t2, t3, t4;
	cin >> t1 >> t2;
	cout << "t1=" << t1;
	cout << "t2=" << t2;
	t3 = t1+t2;
	t4 = t3;
	cout << "t3=" << t3;
	cout << "t4=" << t4;
	system("pause");
	return 0;
}

Answer 1

那是个类，不能相加