3. Errors

  Suppose you ignored the instructions of the previous section and typed a
  non-integer such as 3.4 as input to the program.  Then you would get an
  error, because the ** (to-power) operator is only designed to work when
  the second parameter (that is, the power number) is an integer. You might
  see this, for example:

I     rexx arith
I     3.4
I         6 +++ e=2**(a-1)
I     Error 26 running arith.rexx, line 6: Invalid whole number
O     arith
O     3.4
O          6 +++   e = 2 ** ( a - 1 );
O     REX0026: Error 26 running D:\ARITH.CMD, line 6: Invalid whole number

  Or if you typed zero, you might see the following (because you cannot
  divide by zero):

I     rexx arith
I     0
I         4 +++ c=1/a
I     Error 42 running arith.rexx, line 4: Arithmetic overflow or underflow
O     arith
O     0
O          4 +++   c = 1 / a;
O     REX0042: Error 42 running D:\ARITH.CMD, line 4: Arithmetic 
O     overflow/underflow

  Perhaps most interestingly, if you type a sequence of characters which is
  not a number, you might see this.  It does not complain about the
  characters you entered, but at the fact that the program tries to use it
  as a number.

I     rexx arith
I     hello
I         3 +++ b=a*a
I     Error 41 running arith.rexx, line 3: Bad arithmetic conversion
O     arith
O     hello
O          3 +++   b = a * a;
O     REX0041: Error 41 running D:\ARITH.CMD, line 3: Bad arithmetic conversion

  In each case, you have generated a "syntax error" (it is classified as a
  syntax error, even though the problem was not directly related to the
  program's syntax).  What you see is a "traceback" starting with the line
  which caused the error (no other lines are listed in this traceback,
  because we have not yet considered any Rexx control structures), and a
  description of the error.  This information should help you to determine
  where the error occurred and what caused it.  More difficult errors can be
  traced with the "trace" instruction (see later).