Counting the sum of elements in each column of a two-dimensional array?

Question

C++ / C#

Hello everyone, there is a task to create a dynamic two-dimensional array, calculate the sum, and calculate the sum of the elements in each column. I did almost everything, but I got confused how to correctly calculate the sum of the elements in a column, tell me, please, how to fix it?

#include <iostream>
#include <ctime>
using namespace std;

int main()
{
  srand(time(0));
  int N;
  int M;
  int sum = 0;
  int j = 0;
  cout << "Vvedite N - kolvo strock" << endl;
  cin >> N; 
  cout << "Vvedite M - kolvo stolb" << endl;
  cin >> M;

  int **arr = new int*[N];

  for (int i = 0; i < N; i++)
    arr[i] = new int[M];

  for (int i = 0; i < N; i++)
  {
    for (int j = 0; j < M; j++)
    {
      arr[i][j] = 1 + rand() % 100;
      cout  << arr[i][j]<<"\t";
      sum =sum+ arr[i][j];
      
    }
    cout <<"\n"<< endl;
    cout << "In " << j + 1 << " col sum is " << sum << endl;
  }
  
    cout << sum << "\n";
  for (int i = 0; i < N; i++)
    delete[] arr[i];

  delete[] arr;

  system("pause");
  return 0;
}

Answer 1

Set sum to zero at the beginning of the first loop.
PS: Damn, who teaches you how to make such two-dimensional arrays? Yesterday there was the same question on C++ and the same with similar two-dimensional arrays. Read about address arithmetic or learn how to use standard stl containers so as not to fence this perversion.