CODEWITHSUNDEEP
c++
user1990950
user1990950

Reputation: 35

C++ weird value resetting

When using the code below, it sets the x value of the Tile objects to i and the y value to j. But if I print the values only the y value is correct, the x value is always 4095.

Code:

Main code:

Tile * tiles = new Tile[4096,4096];
    for(int i = 0; i< 4096;i++)
    {
        for(int j = 0;j< 4096;j++)
        {
            tiles[i,j].x = i;
            tiles[i,j].y = j;
        }
    }

    for(int i = 0; i< 4096;i++)
    {
        for(int j = 0;j< 4096;j++)
        {
                cout << "X (Should be " <<i<<"): "<< tiles[i,j].x << " " << "Y (Should be " <<j<<"): "<< tiles[i,j].y << "\n";
        }
    }

Tile.h:

#pragma once

class Tile
{
    public:
        int x, y;
};

Upvotes: 2

Views: 137

Answers (1)

Nemanja Boric
Nemanja Boric

Reputation: 22157

You are not using arrays right:

i,j will always return j, as that is the result of comma operator.

Tile** tiles = new Tile*[4096];
for(int i = 0; i < 4096; i++)
    tiles[i] = new Tile[4096];

    for(int i = 0; i< 4096;i++)
    {
        for(int j = 0;j< 4096;j++)
        {
            tiles[i][j].x = i;
            tiles[i][j].y = j;
        }
    }

    for(int i = 0; i< 4096;i++)
    {
        for(int j = 0;j< 4096;j++)
        {
                cout << "X (Should be " <<i<<"): "<< tiles[i][j].x << " " << "Y (Should be " <<j<<"): "<< tiles[i][j].y << "\n";
        }
    }


   // Destruction! DON'T FORGET!
   for(int i = 0; i < 4096; i++)
       delete[] tiles[i];
   delete[] tiles;

If you calculate values from comma operator, your original code would be:

Tile * tiles = new Tile[4096]; // returned last 4096
    for(int i = 0; i< 4096;i++)
    {
        for(int j = 0;j< 4096;j++)
        {
            tiles[i,j].x = i; // the same as tiles[j].x = i;
            tiles[i,j].y = j; // the same as tiles[j].y = j;
        }
    }

///...

Upvotes: 10

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