The OS reports on errors using error codes.

Here is the list of all error codes and their meanings:

1.  Sys.wait: duration must be positive
2.  Array.new: Illgeal array size
3.  Math.divide: Division by zero
4.  Math.sqrt: Can't compute sqrt of negative numbers
5.  Memory.alloc: Size should be at least 1
6.  Memory.alloc: Heap overflow
7.  Screen.drawPixel: Illegal pixel location
8.  Screen.drawLine: Illegal pixels location
9.  Screen.drawRectangle: Illegal pixels location
12. Screen.drawCircle: Illegal center location
13. Screen.drawCircle: Illegal radius
14. String.new: Illegal string length
15. String.charAt: Index out of bounds
16. String.setCharAt: Index out of bounds
17. String.appendChar: String is at its max length    
18. String.eraseLastChar: String is empty    
19. Output.moveCursor: Illegal cursor location