Why does the second variable not change in the field?

Question

I'm testing some programms for my lectures. I'm creating classes and use a paramterlist to initalize a field but the second variable doesn't change.

#include <iostream>
using namespace std;

class Punkt {

    int x;
    int y;

public:
    Punkt(int a = 0, int b = 0)
    {
        x = a;
        y = b;

    }
    void printXY()
    {
        cout << "x= " << x << " y= " << y << endl;
    }
};

int main() {

    Punkt pFeld[] = { (1, 1), (2, 2), (3, 3) };

    for (int i = 0; i < 3; i++)
        pFeld[i].printXY();
    cin.get();
};

No error messages. Expected result was that x and y change, while actual result is that only x changes and y stays 0.

Answer 1

This

(1, 1)

is an expression with the comma operator.

In fact this initialization

Punkt pFeld[] = { (1, 1), (2, 2), (3, 3) };

is equivalent to

Punkt pFeld[] = { 1, 2, 3 };

So the constructor with the second default argument equal to 0 is called three times.

Use instead

{ 1, 1 }

Here is your updated code

#include <iostream>
using namespace std;

class Punkt {

    int x;
    int y;

public:
    Punkt(int a = 0, int b = 0)
    {
        x = a;
        y = b;

    }
    void printXY()
    {
        cout << "x= " << x << " y= " << y << endl;
    }
};

int main() {

    Punkt pFeld[] = { {1, 1}, {2, 2}, {3, 3} };

    for (int i = 0; i < 3; i++)
        pFeld[i].printXY();
    cin.get();
}

Its output is

x= 1 y= 1
x= 2 y= 2
x= 3 y= 3

Pay attention to that the semicolon after the function main is redundant.