1 REM debug screen
2 CLS
5 LET x=4
6 LET y=30
10 FOR i=0 TO x-1
20 FOR j=0 TO y-1
30 POSITION j,i
40 PRINT "X"
50 POSITION 0,6
60 PRINT i; ", "; j
100 NEXT j
110 NEXT i