C++ multidimensional array capacity

Question

I'm new to C++, and I've started to learn arrays. Here is my program on arrays:

#include <iostream>
using namespace std;
int main(){
    int arr[3][3];

    for (int i = 0; i<3; i++){

        for (int j = 0; j<3; j++){

            cout << "Enter " << j + 1 << " element of " << i + 1 << " row:";
            cin >> arr[i][j];

        }

    }

    for (int i = 0; i<3; i++){

        for (int j = 0; j<3; j++){
            cout << j + 1 << " element of " << i + 1 << "row:";

            cout << arr[i][j] << endl;


        }
    }
    system("pause");
    return 0;
}

I know that array's first index in C++ is zero. So, logically, an array arr[3][3]should have 4 * 4 = 16 elements, right? But practically, if I change 3 to 4 in my for cycles, I'll get out of range error. Why does it happen? Am I missing something? So, how much elemets are in arr[3][3]?

Oh sorry guys for such a question...It was pretty simple... You've made that absolutely clear for me right now! — E_Tony
– E_Tony, Commented Mar 18, 2015 at 16:32

R Sahu · Accepted Answer · 2015-03-18 16:28:53Z

1

So, logically, an array arr[3][3] should have 4 * 4 = 16 elements, right?

That is not correct.

For

int arr[3];

the valid element range is arr[0] - arr[2]. There are 3 elements.

For

int arr[3][3];

the valid element range is arr[0][0] - arr[2][2]. There are 9 elements.

answered Mar 18, 2015 at 16:28

R Sahu

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Comments

user4180612 · Accepted Answer · 2015-03-18 16:28:15Z

1

When you declare an array, you write the number of elements(not counting 0, int arr[3] is an array with 3 elements. Only when you use them, you start counting from 0 (arr[2] = 666 accesses third element).

answered Mar 18, 2015 at 16:28

user4180612

Comments

sam · Accepted Answer · 2015-03-18 16:37:18Z

1

I know that array's first index in C++ is zero.

You are correct.

So, logicaly, an array arr[3][3]should have 4 * 4 = 16 elements, right?

Since first index is 0, arr[3][3] will be 0,1,2 rows and 0,1,2 columns. So, 9 elements enter image description here

Check out this link for tutorials on array (or C++ in general ☺ )

http://www.cplusplus.com/doc/tutorial/arrays/

answered Mar 18, 2015 at 16:37

sam

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