13. WHILE/WEND Loops

Imagine that you want to check the tyre pressure for lorries and motor bikes, as well as for four-wheeled cars. (See Sec..) The algorithm to do this is something like:

CHECK IF THERE ARE MORE TYRES LEFT
MOVE TO NEW TYRE
MEASURE PRESSURE IN TYRE
GO BACK TO START

As can be seen, the above program/algorithm keeps going around in a loop so long as a certain condition is satisfied (i.e. so long as there are more tyres to be checked). Basic has a loop in exactly this style.

Consider the following program (note that str_My_Number should be the name of a text box):

My_Number = Val(str_My_Number)

i = 0

While i <> My_Number
i = i + 1
Wend

Print "I think that your number is "; i

In this example, the loop begins with While and ends with Wend. Inside this While loop the variable i is increased by one each time through the loop. The While loop stops when i is equal to My_Number. Note that the symbol <> means "not equal to" (see ). A working version of this programme appears here.

You can see that in this case the For/Next loop is of no use since you don't know in advance how many times you want to go around the loop.

While loops are similar to For/Next loops in that they are used when the same lines of code need to be repeated more than once. However While loops are typically more flexible - the loop stops when some condition is no longer satisfied.