Fill a symmetric matrix in c++

Question

having a trouble with a condition which tells if an element of a multidimensional array
as example arr[row][col] is exactly arr[col][row] then automatically assign the value of arr[col][row] to the same value of arr[row][col] without letting user enter it manually

That should be an example of the output

example[4][4] = 
     {
     //   0   1   2   3
        { 0, 10, 15, 18},   //   0
        { 10, 0, 20, 14},   //   1
        { 15, 20, 0, 90},   //   2
        { 18, 14,90, 0},    //   3

here's my code

`   int size;
    int arr[size][size];
    cout<<"Choose size of your multidimensional array [matrix]: ",cin>>size;
    cout<<"Now enter your data [Respectively] \n";
    for(int d=0 ; d<size ; d++)
    {
        for(int j=0; j<size; j++)
        {
            if (d==j) 
            {
                arr[d][j]=0 ;
            }
            else if(arr[d][j]!=0 ) //there should be the problem
            {
                arr[j][d]=arr[d][j];
            }
            else
            {
                cin>>arr[d][j]; // Filling matrix
            }
        }
    }  `

Answer 1

Here is a Minimum Working Example (MWE) that should solve your issues:

#include <iostream>

using namespace std;

int main()
{
    cout << "Choose size of your multidimensional array [matrix]: ";
    int size;
    cin >> size;
    int arr[size][size];
    cout << "Now enter your data [Respectively] \n";
    for(int d=0; d<size; d++)
    {
        for(int j=d+1; j<size; j++)
        {
            if (d==j)
            {
                arr[d][j] = 0;
            }
            else if(j<d)      // here laid the problem
            {
                arr[d][j] = arr[j][d];
            }
            else
            {
                cin >> arr[d][j]; // Filling matrix
            }
        }
    }

    // print matrix
    for(int d=0; d<size; d++) {
        for(int j=0; j<size; j++)
            cout << arr[d][j] << " ";
        cout << '\n';
    }

return 0;
}

This below is even cleaner, gets rid of the conditional inside the inner loop, thank you @ThomasSablik

#include <iostream>

using namespace std;

int main()
{
    cout << "Choose size of your multidimensional array [matrix]: ";
    int size;
    cin >> size;
    int arr[size][size];
    cout << "Now enter your data [Respectively] \n";

    for(int d=0 ; d<size ; d++)
    {
        arr[d][d]=0;
        for(int j=d+1; j<size; j++)
        {
            cin >> arr[d][j];
            arr[j][d]=arr[d][j];
        }
    }

    // print matrix
    for(int d=0; d<size; d++) {
        for(int j=0; j<size; j++)
            cout << arr[d][j] << " ";
        cout << '\n';
    }

return 0;
}