Answer 1

It's similar to the way with any other loop structure. This is one simple way to do it:

public class Program {
public static void main(String[] args) {
int size = 5;
int row = 0;
int col = 0;

do { // Print rows
do { // Print columns
System.out.print(col);
col++;
} while (col <= row);
System.out.println(); // New row
col = 0; // Going to the first column
row++;
} while (row < size);
}
}