VBScript conditional logic
You can implement VBScript code which makes decisions based on certain things using conditional logic.
This lesson focuses on:
- The if statement
- The else statement
- The elseif statement
- Using if, else, and elseif together
- The Select statement
The if statement
The if statement tests if a certain condition is true or false and acts upon it accordingly.
Syntax:
if condition then perform this action end if
If the specified condition is true, then the code following the condition will be executed, otherwise it will not.
Example:
<script type="text/vbscript">
Dim aNumber
aNumber= 5
if aNumber = 5 then
document.write("aNumber is equal to 5")
end if
</script>
Output:
The else statement
If the condition in an if statement is true, then the code following the condition will be executed. But what if you wanted something to happen if it is false? What if you wanted one thing to happen if the condition is true, and something else to happen if the condition is false? This is where the else statement comes in. The else statement works in conjunction with the if statement and executes certain code if the condition in the if statement is false.
Syntax:
if condition then perform this action else perform this action if the above condition is false end if
If the condition in the if statement is false, then the action dictated by the else statement will be performed.
Example 1:
<script type="text/vbscript">
Dim plant
plant = "cactus"
if plant = "cactus" then
document.write("Great choice!")
else
document.write("Still a good choice, though cactuses
are better.")
end if
</script>
Output:
Example 2:
<script type="text/vbscript">
Dim plant = "birch"
if plant = "cactus" then
document.write("Great choice!")
else
document.write("Still a good choice, though cactuses
are better.")
end if
</script>
Output:
The elseif statement
The if statement tests a single condition and performs an action if that condition is true and the else statement performs an action if the condition in the if statement is false, but what if there are more than two possibilities? Surely, any condition can be only true or false, but what if you needed to test a variable for more than one value? This is where the elseif statement comes in. The elseif statement is used in conjunction with the if statement. Unlike the else statement, it does not specifically perform a certain action if the condition in the if statement is false, but rather it performs an action if the condition in the if statement is another specific value specified in the elseif statement itself.
Syntax:
if condition is one value then perform this action elseif condition equals another value then perform this action end if
Example:
<script type="text/vbscript">
Dim X
X = 7
if X = 5 then
document.write("X is equal to 5")
elseif X = 7 then
document.write("X is equal to 7")
end if
</script>
Output:
In the above example, we are testing if the variable X is equal to 5, and if it is, print the message "X is equal to 5". We then use the elseif statement to test if the variable X is equal to 7, and if it is, print the message "X is equal to 7".
Using if, else, and elseif together
You can use the if, else, and elseif statements together when you want to check a variable for a certain value many times. If it is not any of the checked values then the code specified by the else statement will be executed.
Syntax:
if condition then perform this action elseif condition equals another value then perform this action elseif condition equals another value then perform this action elseif condition equals another value perform this action else if the condition was not equal to any of the values tested in the if statement and all the elseif statements, then perform this action end if
Example:
<script type="text/vbscript">
Dim X
X = 5
if X = 9 then
document.write("X is equal to 9")
elseif X = 7 then
document.write("X is equal to 7")
elseif X = 3 then
document.write("X is equal to 3")
elseif X = 15 then
document.write("X is equal to 15")
else
document.write("X is not equal to 9, 7, 3, or 15. X is equal
to " & X);
end if
</script>
Output:
The Select statement
The Select statement is specifically designed for comparing one variable to a number of possible values. It can be thought of as a substitute for the if, elseif, else structure.
Syntax:
select case variable case possible value perform this action case possible value perform this action case possible value perform this action case possible value perform this action case else perform this action if none of the values match end select
Example:
<script type="text/vbscript">
Dim X
X = 7
select case X
case 1
document.write("X is equal to 1")
case 2
document.write("X is equal to 2")
case 3
document.write("X is equal to 3")
case 7
document.write("X is equal to 7")
case else
document.write("X is not equal to
any of the values specified")
end select
</script>
Output:
In the above example, the variable X is initialized to 7, and is tested for a number of values. If X is equal to 1, the message "X is equal to 1" will be printed. If X is equal to 2, the message "X is equal to 2" will be printed. If X is equal to 3, the message "X is equal to 3" will be printed. If X is equal to 7, the message "X is equal to 7" will be printed. If X is equal to neither 1, 2, 3, or 7, the message "X is not equal to any of the values specified" will be printed.
