XL: Using the Imp Operator for Binary Comparison

Last reviewed: February 27, 1998
Article ID: Q168344
The information in this article applies to:
  • Microsoft Excel 97 for Windows
  • Microsoft Excel for Windows 95, version 7.0
  • Microsoft Excel for Windows, version 5.0

SUMMARY

The Visual Basic for Applications Imp operator is used to perform a logical implication on two expressions. If you are using the Imp operator with two numeric expressions as arguments, Microsoft Excel performs a bit-wise comparison of identically positioned bits.

MORE INFORMATION

The syntax for the Imp operator is as follows

   <result> = <expression1> Imp <expression2>

where <expression1> and <expressions2> are any expressions and <result> is any numeric variable.

When you use the Imp operator to perform a bit-wise comparison of identically positioned bits in two numeric expressions, the result of the bit-wise comparison is determined using the rules in the following table.

   Bit in Expression1   Bit in Expression2   Bit in Result
   -------------------------------------------------------

           1                     1                 1
           1                     0                 0
           0                     1                 1
           0                     0                 1

Microsoft provides examples of Visual Basic for Applications procedures for illustration only, without warranty either expressed or implied, including, but not limited to the implied warranties of merchantability and/or fitness for a particular purpose. The Visual Basic procedures in this article are provided 'as is' and Microsoft does not guarantee that they can be used in all situations. While Microsoft support engineers can help explain the functionality of a particular macro, they will not modify these examples to provide added functionality, nor will they help you construct macros to meet your specific needs. If you have limited programming experience, you may want to consult one of the Microsoft Solution Providers. Solution Providers offer a wide range of fee-based services, including creating custom macros. For more information about Microsoft Solution Providers, call Microsoft Customer Information Service at (800) 426-9400.

For example, if you run the following macro, a message box displays the value of -11:

   Sub Imp_Example()

   Dim a As Integer
   Dim b As Integer
   Dim result As Integer

      a =10
      b = 4

      result = a Imp b

      MsgBox result

   End Sub

The value -11 is returned because the macro follows the rules in the table and uses twos complement notation. Using twos complement notation, the leftmost bit represents the sign bit. If this bit is one, the number is negative; if this bit is zero, the number is positive. To convert a negative number from binary back to decimal, complement all of the bits (1 becomes 0 and 0 becomes 1), convert that number to decimal, change the sign of the decimal number, and then subtract 1.

In the example, the Imp operator is used with the two numeric values 10 and 4. In binary form (2 bytes), these two numbers appear as follows:

   10:   0000000000001010
    4:   0000000000000100

Using the bit-wise comparison rules from the table yields the result value in binary form:

   10:   0000000000001010
    4:   0000000000000100
   --------------------------

   result:   1111111111110101

To determine the decimal equivalent of result, use the twos complement rules of conversion as follows:

                                     Result: 1111111111110101
                        Complement each bit: 0000000000001010
   Decimal equivalent of this binary number: 10
                    Opposite of this number: -10
       Subtract 1 (decimal value of result): -11

REFERENCES

For more information about the Imp Operator, click the Index tab in Visual Basic for Applications Help, type the following text

   imp

and then double-click the selected text to go to the "Imp Operator" topic.


Additional query words: 5.00 7.00 97 XL97
Keywords : kbprg kbhowto
Version : WINDOWS:5.0,7.0,97
Platform : WINDOWS
Issue type : kbinfo


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Last reviewed: February 27, 1998
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