This is just one of many possible solutions:

```
when green flag clicked
set [black cards total v] to [0]
set [row number v] to [1]
ask [How many rows would you like to enter?] and wait
set [number of rows v] to (answer)
repeat (number of rows)
set [index v] to [1]
ask (join (join (join [Please enter ] (number of rows)) [ cards for row ]) (row number)) and wait
set [row v] to (answer)
repeat (length of (row))
if <(letter (index) of (row)) = [B]> then
change [black cards total v] by (1)
end
change [index v] by (1)
end
if <((black cards total) mod (2)) = [0]> then
say (join (join [Row ] (row number)) [ is OK!]) for (2) secs
else
say (join [There is a parity error is row ] (row number)) for (2) secs
end
change [row number v] by (1)
set [black cards total v] to [0]
end
```