Question

I have small issue. I create 2D int array. When I cout it I get hexadecimals numbers insted of decimals. I’m using Dev C++.

#include <cstdlib>
#include <iostream>

using namespace std;

int main()
{
    const int max=9;
    int ar[max][max]={
        {0,6,0,0,2,0,0,4,0},
        {5,0,0,3,0,0,0,0,0},
        {0,8,0,0,1,0,0,0,0},
        {6,0,0,0,0,7,0,0,0},
        {0,3,7,0,0,0,2,8,0},
        {0,2,0,8,0,0,0,3,0},
        {0,0,0,0,0,0,0,0,0},
        {7,0,0,4,0,0,0,0,1},
        {0,0,0,0,6,0,0,2,0}};

    for (int i=0;i<max;i++){
        for(int j=0;j<max;j++){
            cout<<ar[i,j]<<" ";
        }
        cout<<"\n";
    }

    system("pause");
    return 0;
}

In return I get this http://www.dropmocks.com/mf8wl

Answer 1

That’s because you’ve fallen into the cunning trap of operator ,!

First of all, C doesn’t have multi-dimensional arrays as a primitive. As you’ve declared here, a 2D array is just “an array of arrays”. Therefore, it makes no sense to access an array with a[i,j]. You should first get the “row” with a[i] then index the “column” with [j], whence a[i][j].

So, why does your code compile? Because the , is an operator in C. The evaluation of a,b is effectively the evaluation of expression a, then b, returning the result of evaluating b. Hence you’re actually printing a[j] here, which is an int[], printed in hex as the address of the array.

Why have an operator , at all, you ask? Other than to be confusing, it’s mostly for constructs like for, where you might want multiple expressions in an initialiser or incrementation construct, i.e. for (j = 0, i = 0; i + j < k; i++, j += 2) or similar.