Addition of a Matrix in C++ || Simple Code

/*{

    #include <iostream>
    #include <math.h>
    using namespace std;
    int main()
    {
      int n, sum = 0;
      cout << "Enter the size of square matrix" << endl;
      cin >> n;
      int aar[20][20];
      cout << "Enter the element of matrix" << endl;
      for (int i = 0; i < n; i++)
      {
        for (int j = 0; j < n; j++)
        {
          cin >> aar[i][j];
        }
      }
      for (int i = 0; i < n; i++)
      {
        sum = 0;
        for (int j = 0; j < n; j++)
        {
          sum += aar[j][i];
        }
        aar[n][i] = sum;
        cout << endl;
      }
      for (int i = 0; i < n; i++)
      {
        sum = 0;
        for (int j = 0; j < n; j++)
        {
          sum += aar[i][j];
        }
        aar[i][n] = sum;
        cout << endl;
      }
      sum = 0;
      for (int i = 0; i < n; i++)
      {
        sum += aar[n][i];
      }
      aar[n][n] = sum;
      cout << "Resultant Matrix :- " << endl;
      for (int i = 0; i <= n; i++)
      {
        for (int j = 0; j <= n; j++)
        {
          cout << aar[i][j] << " ";
        }
        cout << endl;
      }

      return 0;
    }

When the above program is executed, it produces following results --<\b>

    Enter the size of square matrix
    3
    Enter the element of matrix
    2 2 2 1 1 1 3 3 3


    Resultant Matrix :- 
    2 2 2 6 
    1 1 1 3 
    3 3 3 9 
    6 6 6 18 

}*/