Set outer to the value that should fill the box border.
FOR row in range 0 to 2*outer-1
Set row_val to the absolute value of row - (outer-1)
FOR col in range 0 to 2*outer-1
Set col_val to the absolute value of col - (outer-1)
Output the greater of col_val and row_val
END FOR
Ouput a newline
END FOR