How to Use UDF() to Modify Default Scientific Notation Format

ID: Q148784

2.00 2.5x 2.60 2.60a | 2.5x 2.60 2.60a 3.00 3.00b | 2.5x 2.60a | 2.60

MS-DOS               | WINDOWS                    | MACINTOSH  | UNIX
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The information in this article applies to:

Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b
Microsoft FoxPro for MS-DOS, versions 2.0, 2.5, 2.5a, 2.5b, 2.6, 2.6a
Microsoft FoxPro for Windows, versions 2.5, 2.5a, 2.5b, 2.6, 2.6a
Microsoft FoxPro for Macintosh, versions 2.5b, 2.5c, 2.6a
Microsoft FoxPro for UNIX version 2.6

SUMMARY

The default formatting that Visual FoxPro applies to numbers requiring scientific notation does not conform to a standard that many customers expect. You can use the user-defined function (UDF) in this article to address this issue.

MORE INFORMATION

The following program is a UDF() that can process a numeric value into the standard format expected by many customers who have expressed a need for an alternative format for scientific notation:

PARAMETERS   nPassedVal

* Program:   Num2sci.prg
*
* Purpose:   Convert FoxPro formatted numeric values requiring scientific
*            notation to the frequently requested n.nnnE+n format.
* Syntax:    NUM2SCI(nExpression)

* Arguments: nExpression is the numeric value to convert to the alternative

*            format.
* Returns:   Character

* Important notes about minimum and maximum ranges FoxPro will address: * ------------------------------------------------------------------------- * SET DECIMALS makes no difference to any of this functionality. * FoxPro will round values beginning at the fifteenth decimal place. * Margin of error at 15 decimals or more is 3.410910030699E-15. * The maximums for the STR() function are: STR(n,25,18). * * Any value of n.nE+19 or greater will resolve to scientific notation. * * Ex: ALLTRIM(STR(1.234567890e+18,25,18))

*       Resolves to: "1234567890000000000.00000"

* Ex: ALLTRIM(STR(1.234567890e+19,25,18))

*       Resolves to: ".1234567890000004000E+20"
*

* Any value passed with n.nE-16 or lower will resolve to equal zero. * * Ex: ALLTRIM(STR(1.234567890e-15,25,18))

*       Resolves to: "0.000000000000001000"

* Ex: ALLTRIM(STR(1.234567890e-16,25,18))

*       Resolves to: "0.000000000000000000"
*

* These are limitations in FoxPro that cannot be changed. This procedure, * and therefore any data it processes, is limited to working within these * constraints. * * -------------------------------------------------------------------------

* Stage 1: Convert to character cConvStage1 = UPPER(ALLTRIM(STR(nPassedVal,25,18))) * Find initial location of decimal point nDecimalLoc = ATC(".", cConvStage1) * Find 'E' beginning notation

nExpLoc     = RAT("E", cConvStage1)

IF nExpLoc = 0                           && No notation in resolved value.
  * Remove trailing zeros from character value
  DO WHILE SUBSTR(cConvStage1,LEN(cConvStage1),1) = '0'
    cConvStage1 = SUBSTR(cConvStage1,1,LEN(cConvStage1)-1)
  ENDDO
  cRetVal = SUBSTR(cConvStage1,1)    && Return entire number included.

decimals ELSE * Stage 2: Value deconstruction and element reformatting * Swap positions of first two characters

  cConvStage2a = SUBSTR(cConvStage1,2,1)+"."
  * Portion between the decimal and the 'E'
  cConvStage2b = SUBSTR(cConvStage1,3,nExpLoc-3)
  * Decrement notation by 1
  cConvStage2c = "E+"+ALLTRIM(STR(VAL(SUBSTR(cConvStage1,nExpLoc+2))-1))

  * process portion between decimal and the 'E' to remove trailing Zeros
  DO WHILE SUBSTR(cConvStage2b,LEN(cConvStage2b),1) = '0'
    cConvStage2b = SUBSTR(cConvStage2b,1,LEN(cConvStage2b)-1)
  ENDDO

  * Stage 3: Value reconstruction
  cRetVal = cConvStage2a+cConvStage2b+cConvStage2c

ENDIF RETURN cRetVal

To convert the value back to numeric, use the VAL() function against the character data NUM2SCI() returned.

Additional reference words: 2.00 2.50 2.60 2.60a 3.00 3.00b FoxWin FoxMac FoxUnix FoxDos VFoxWin KBCategory: kbhowto KBSubcategory: FxprgGeneral

Keywords          : kbcode FxprgGeneral 
Version           : 2.00 2.5x 2.60 2.60a | 2.5x 2.60
Platform          : MACINTOSH MS-DOS UNIX WINDOWS