String Comparison Operation

VBScript Tutorials - Herong's Tutorial Examples

∟String Operations - Concatenation and Comparison

∟String Comparison Operation

This section provides a quick introduction of string comparison operations, which compare one character at a time based its ASCII value.

String comparison operations are operations that:

Operates on two operands of String values.
Produces a Boolean value by applying the string comparison operation specified by the operator.
String comparison operations are performed one character at a time with its ASCII value.
String comparison operations use same operators as numeric comparison operations: =, <>, <, >, <=, >=.

There are 6 string comparison operations supported in VBScript:

Equal to (=): Resulting (True) if two strings have the same length and the same characters at the same positions.
Not equal to (<>): Resulting (True) if two strings are not equal.
Greater than (>): Resulting (True) if the first string is greater than the second string. The logic of (>) operation works by comparing every character in the first string with the character at the same position in the second string from left to right. If there is no character left in the second string, stop operation and return (True); Or if the character in the first string has a higher ASCII value, stop operation and return (True); Or if two characters are identical, continue to the next character; Otherwise, stop operation and return (False).
Less than (<): Resulting (True) if two strings are not equal, and the first string is not greater than the second string.
Greater than or equal to (>=): Resulting (True) if the first string is greater than the second string or two strings are equal.
Less than or equal to (<=): Resulting (True) if the first string is less than the second string or two strings are equal.

To show you how string operations work, I wrote the following script, string_comparison.html:

<html>
<body>
<!-- string_comparison.html
 - Copyright (c) 1998 HerongYang.com. All Rights Reserved.
-->
<pre>
<script language="vbscript">
   document.writeln("ABC" = "abc")
   document.writeln("ABC" <> "abc")
   document.writeln("abc " > "abc")
   document.writeln("abc" < "abc")
   document.writeln("abc" >= "abd")
   document.writeln("abc" <= "abc")
</script>
</pre>
</body>
</html>

Here is the output of this VBScript example script:

False
True
True
False
False
True

The output confirms some of string comparison operation rules:

("ABC" = "abc") returns False, because the first character of the first operand is not equal to the first character of the second operand.
("abc " > "abc") returns True, because the first operand has one more character than the second operand, and all other 3 characters are identical in both operands.