Ruby program to print the left diagonal matrix

TwoDArr = Array.new(3){Array.new(3)}

printf "Enter elements of MATRIX:\n";
i = 0;
while (i < 3) 
  j = 0;
  while (j < 3) 
    printf "ELEMENT [%d][%d]: ", i, j;
    TwoDArr[i][j] =  gets.chomp.to_i;
    j = j + 1;
  end
  i = i + 1;
end

printf "MATRIX:\n";
i = 0;
while (i < 3)
  j = 0;
  while (j < 3) 
    print TwoDArr[i][j]," ";
    j = j + 1;
  end
  i = i + 1;
  print "\n";
end

printf("Left diagonal of matrix:\n")
i = 0;
while (i < 3) 
    j = 0;
    while (j < 3) 
        if (i == j)
          printf "%d ", TwoDArr[i][j];
        else
          printf(" ");
         end
        j = j + 1;
    end
    i = i + 1;
    print "\n";
end

Output:

Enter elements of MATRIX:
ELEMENT [0][0]: 1
ELEMENT [0][1]: 2
ELEMENT [0][2]: 3
ELEMENT [1][0]: 4
ELEMENT [1][1]: 5
ELEMENT [1][2]: 6
ELEMENT [2][0]: 7
ELEMENT [2][1]: 8
ELEMENT [2][2]: 9
MATRIX:
1 2 3 
4 5 6 
7 8 9 
Left diagonal of matrix:
1   
 5  
  9