How to fill a 2D through input and then read back as output in a C++. Here is the code which I wrote. I gives wrong output.I am a beginner

Question

#include <iostream>
#include<fstream>

using namespace std;

int main() {
    int a = 1;

    if (a == 1) {
        int a[1][1];
        for (int i = 0; i <= 1; i++) {
            for (int j = 0; j <= 1; j++) {

                cin >> a[i][j];
            }
        }
        cout << endl;

        for (int k = 0; k <= 1; k++) {

            for (int l = 0; l <= 1; l++) {
                cout << a[k][l] << "   ";
            }
            cout << endl;
        }


    }

    return 0;
}

In this program if we enter input as : 1 2 3 4

it gives output : 1 3 3 1 it should give output as: 1 2 3 4 Please help, I am a beginner. I am coding in code blocks.

`int a[1][1];` has a single element. Its only valid index is `a[0][0]`. All your loops go out of bounds and invoke undefined behavior. Change `for(int k=0;k<1;k++)` — 463035818_is_not_an_ai, Dec 18 '20 at 10:38
it is unfortunate that the same syntax is used for different things. `int a[1][1];` declares an array with 1 element, but `int x = b[1][1];` accesses the second element in the second subarray of `b` — 463035818_is_not_an_ai, Dec 18 '20 at 10:39
@largest_prime_is_463035818 Actually, they should change array to 2x2: `int a[2][2];`, they want to store 4 inputs. — Yksisarvinen, Dec 18 '20 at 10:40
@Yksisarvinen right, maybe `for(int k=0; k < SIZE; k++)` would have been more clear — 463035818_is_not_an_ai, Dec 18 '20 at 10:41
When declaring an array, the size is the number of elements, not the top index. — Some programmer dude, Dec 18 '20 at 10:41
fwiw, using `std::array` (or `std::vector`) helps to avoid this and uncountable other problems — 463035818_is_not_an_ai, Dec 18 '20 at 10:42
You really should invest in [some decent books](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list), and maybe even take a class or two? — Some programmer dude, Dec 18 '20 at 10:44
Here, `int a[1][1];` defines only one element. You have to define as `int a[2][2];` to store 2x2 array. — Krishna Kanth Yenumula, Dec 18 '20 at 10:48

score 0 · Accepted Answer · answered Dec 18 '20 at 11:16

Try this

int main()
{
int arr[2][2]; // declares a 2x2 array

    cout << "Enter integers : " << endl;
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 2; j++) {
            cin >> arr[i][j]; //inserts at the index i and j in the array
        }
    }

    cout << "Display array : " << endl;
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 2; j++) {
            cout << arr[i][j] << endl; /*displays the value at 
            index i and j in the array*/
        }
    }
}

How to fill a 2D through input and then read back as output in a C++. Here is the code which I wrote. I gives wrong output.I am a beginner

1 Answers1