Q11697: Integer "Overflow" Is Not Trapped without /D Debug Switch

Article: Q11697
Product(s): See article
Version(s): 1.00 1.01 1.02 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | b_basiccom | mspl13_basic
Last Modified: 20-JUL-1989

The following program returns the error "Overflow in line 20 of module
at address xxxx:xxxx" when compiled with the /D switch:

   10  x% = 129
   20  print 256 * x%
   30  end

If the sample program is compiled without the /D switch, no error is
reported, but an incorrect (negative) value is returned.

Forcing "256" to single precision by using 256! or 256.0 will
eliminate the overflow error. "256" is an integer, and the result of
129 times 256 is greater than 32,767, which is the highest integer
allowed.

This information applies to Microsoft QuickBASIC Versions 1.00, 1.01,
1.02, 2.00, 2.01, 3.00, 4.00, 4.00b, and 4.50 for MS-DOS and to
Microsoft BASIC Compiler Versions 6.00 and 6.00b for MS-DOS and MS
OS/2.

These compilers don't handle type coercion, nor do they check for
overflow unless the program was compiled with the /D switch.

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