XL: Using the Imp Operator for Binary Comparison

ID: Q168344

The information in this article applies to:

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

Microsoft provides programming examples 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. This article assumes that you are familiar with the programming language being demonstrated and the tools used to create and debug procedures. Microsoft support professionals can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific needs. If you have limited programming experience, you may want to contact the Microsoft fee-based consulting line at (800) 936-5200. For more information about the support options available from Microsoft, please see the following page on the World Wide Web: 

   http://www.microsoft.com/support/supportnet/refguide/
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
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 kbdta KbVBA kbhowto 
Version           : WINDOWS:5.0,7.0,97
Platform          : WINDOWS
Issue type        : kbinfo

Last Reviewed: May 18, 1999