DSA Wave print a Matrix or 2D Array

Using C++

#include <iostream>
using namespace std;

int main() {

  // wave print a matrix
  int arr[3][3] = {{1, 2, 3}, {4, 5, 6}, {10, 11, 12}};
  //print normal array 
  for (int r = 0; r < 3; r++) {
    for (int c = 0; c < 3; c++) {
      cout << arr4[r][c] << " ";
    }
    cout << endl;
  }
  cout << endl;

  //print array column wise
  for (int c = 0; c < 3; c++) {
    for (int r = 0; r < 3; r++) {
      cout << arr4[r][c] << " ";
    }
    cout << "--";
  }
  cout << endl <<endl;
  
  //print array in wave
  for (int c = 0; c < 3; c++) {
    int r;
    // even column 0, 2
    if (c % 2 == 0) {
      for (int r = 0; r < 3; r++) {
        cout << arr4[r][c] << " ";
      }
    } else {
      for (int r = 2; r >= 0; r--) {
        cout << arr4[r][c] << " ";
      }
    }

    cout << endl;
  }

  return 0;
}