ASP: Constants

In our Variables tutorial we have shown you, how variables are used as containers to store information. Well so does a constant. The main difference between constants and variables is that constant value can not be changed in the process of running program. Constants always keep their value assigned while declaration.

Have a look at the following example where  the value of the myText variable changes throughout the script.

'commented lines starting with an apostrophe
'are not executed in VBScript
'first we will declare a variable

Dim myText
'Let's assign a value to our variable
myText = "Good Morning!"
'now the myText variable contains the value Good Morning
'the output will be Good Morning
'next we will assign a new value to our variable

myText = "Have a nice day!"
'now the myText variable contains the value Have a nice day
'the output will be Have a nice day

The value stored in a constant cannot be changed after it has been declared.  If we attempt to re-assign the value of the constant as we did with the value of the variable we’ll get a run time error. To declare a constant in VBScript we use the Const keyword.

'the constant is declared and assigned the value all on the same line
Const myConst = myText"
'it is allowed to declare a few constants on the one line
Const PI = 3.14159, Wg  = 2.78

The following example demonstrates the advantage of constants: during the calculations with number PI, you can type in your code only constants name instead of typing this number each time.


vCircle = PI * vRadius^2



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