In my tryst with QTP for last 8, I have came across many
people aspiring to use Do…while/Do…Until in their code but are surrounded with
lots of confusion or lack of know how. Pavan (my buddy) is not an exception. He
hasn’t used Do…Until in his programming so far and seems to be gravely
obsessed with it. This post is for him and for any one who want to crack the
Do..While/Do..Until riddle.
Let’s get started.
For loop is used in QTP (or VB for that matter) is used when
a block of code need be repeated for certain number of times – but what if the
number of lines of code that need to be repeated is based on certain condition
or conditions. The Do…While and Do…until comes to rescue. These statements
enables you to repeat a set of code while a certain condition is True, or until
a certain condition is True.
Example Time:
Suppose you want to add series of numbers but you wouldn’t like
to do it infinitely. So, a restrictive condition should be required say, sum
shold not exceed 100.
Dim sum = 1
Do While sum < 100
sum = sum + 10
Loop
Generic Version
Do While (Conditional statement)
Some code…( is executed while
conditional statement is TRUE)
Loop
In this code, the Do…While loop evaluates the variable ‘sum ‘every
time to check whether it is less than 100. If it is, the next chunk of code is
run. If not, it moves to the next line of code following loop. The loop keyword
tells the code to go back to the Do.. While line and evaluate the new value of
sum.
Note: Multiple conditions can be added in Do…While using AND
operator.
Unlike, the Do…While statement repeats a loop while the
condition is true, the Do…Until statement repeats a loop until a condition
becomes true.
Example Time:
Dim sum = 1
Do Until sum >= 100
sum = sum + 10
Loop
Generic Version
Do Until (Conditional statement)
Some code…( is executed until the conditional statement becomes TRUE)
Loop
The block of code resembles the Do…While statement, except
that this time the code is evaluating the sum variable to check whether it is
greater than equal to 100.
Please also note that there can be a natural variation of
these loop statements as following.
Do
some code …
Loop While i>10
------------
Do
some code …
Loop Until i=10
I think it is evident that set of code is executed at least
once without evaluation of condition and next iteration is dependent on
True/False of condition.
