Q28164: Unexpected PRINT USING ".##" Rounding for .xx5
Article: Q28164 Product(s): See article Version(s): 4.00 4.00b 4.50 Operating System(s): MS-DOS Keyword(s): ENDUSER | B_BasicCom | mspl13_basic Last Modified: 14-FEB-1991 This article describes a case where the PRINT USING statement appears to round numeric constants to unexpected values. This information applies to Microsoft QuickBASIC versions 4.00, 4.00b, and 4.50 for MS-DOS; to Microsoft BASIC Compiler versions 6.00, 6.00b for MS-DOS and MS OS/2; and to Microsoft BASIC Professional Development System (PDS) versions 7.00 and 7.10 for MS-DOS and MS OS/2. For the following statement PRINT USING " ###.##"; .245, .255, .265, .275, .285 the above BASIC versions give the following output 0.25 0.25 0.26 0.28 0.28 while you might have expected the following rounding 0.25 0.26 0.27 0.28 0.29 or with IEEE rounding (to the nearest even integral value), you would expect the following: 0.24 0.26 0.26 0.28 0.28 This behavior occurs because the internal representation of the numbers used by BASIC (IEEE floating-point format) differs slightly from the decimal numbers typed into the source code. IEEE floating-point format cannot accurately represent numbers that are not of the form 1.x to the power of y (where x and y are base 2 numbers). The internal representation will be slightly more or slightly less than the decimal numbers typed into the source code. The internal representations are correctly rounded and displayed in the above program. This is not a software problem. If you want floating-point constants in the source code to be exactly stored, you can append the constant with the CURRENCY type-cast operator, an "at sign" (@) character. The CURRENCY data type is only found in Microsoft BASIC PDS 7.00 and 7.10. The following example rounds to 0.25, 0.26, 0.27, 0.28, 0.29 as you may have wanted: PRINT USING " ###.##"; .245@, .255@, .265@, .275@, .285@ Note that the CURRENCY data type can store 19 digits, but only 4 digits can be used after the decimal point.
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