How can I enter (i+1) as a string?

Question

How can I enter (i+1) as a string? I would want to print out this array to show list 1 column from 1-7, and the rest of the columns to be a,b,c,d.

void fillArray(string a[][5], int x)
{

  for (int i = 0; i < 7; i++)
  {
    a[i][0] = (i + 1);
    a[i][1] = "A";
    a[i][2] = "C";
    a[i][3] = "B";
    a[i][4] = "D";
  }
}