C++ "Cộng trừ số phức + đa năng hóa toán tử"

#include <iostream>
using namespace std;

typedef struct SP{
    double rel;
    double img;
} SP;

SP setSP(int _rel, int _img);
void display(SP c);
SP operator + (SP c1, SP c2); // overload +
SP operator - (SP c1, SP c2); // overload -

int main(){
    SP c1, c2, c3, c4;
    c1 = setSP(1, -2);
    c2 = setSP(3, 4);
    c3 = c1 + c2;
    printf("Tong hai so: "); display(c3);
    c4 = c1 - c2;
    printf("Hieu hai so: "); display(c4);
    return 0;
}

SP setSP(int _rel, int _img){
    SP c;
    c.rel = _rel; c.img = _img;
    return c;
}

void display(SP c){
    cout << c.rel <<" + i*" << c.img << endl;
}

SP operator + (SP c1, SP c2){
    SP c;
    c.rel = c1.rel + c2.rel;
    c.img = c1.img + c2.img;
    return c;
}

SP operator - (SP c1, SP c2){
    SP c;
    c.rel = c1.rel - c2.rel;
    c.img = c1.img - c2.img;
    return c;
}