Decision Making and Looping

Looping

Many a time you have to perform a programming task again and again. For example, the program should keep reading the data rows of a database file until it encounters the end of the file. Or, a shopping cart script should keep adding items to the cart until the user clicks on "checkout" button.

Primarily, in VBScript, there are four loop structures, namely, for…next, do…until…loop, while…wend, and do…while…loop. Let us see them one by one…

The for…next loop is typically used when the loop has to happen according to some number, and not a criteria. For instance,

But it doesn't mean the other loop structures cannot handle number-based loops. We can have the above loop with do…until too.



While loops are somewhat more sophisticated. In while loops, you can decide whether you necessarily want to execute the code within the while loop or not. The below example explains it properly.



By the end of the loop, the variable i will have value 1 even when its condition of CarryOn being true is not met with. Again,



In the above example, the variable i will contain 0 (zero) because it is in the beginning itself when it is checked what sort of value CarryOn has.

The usage of different while loop structures depends on your preferences and need and you can use most of the loops in any way.

A working example of if-then-else-end-if and looping combined.

In this example, the program counts how many times a particular alphabet appears in a given string. It also highlights the found alphabet in the string.



You may notice some new string-handling functions - len() and mid() - but we shall discuss them at the appropriate time.