In the do...while loop,
the code block is executed
without any checks at the beginning.
The loop condition is checked
after the code block is executed.
If the condition evaluates to true,
the loop moves to its next iteration.
If the condition evaluates to false,
then the execution of the loop is stopped.
Let's look at the example given below,
where we print the numbers from 1 to 5
using a do...while loop.
Here, we first initialize
a variable iteration
with the value 1.
We then start a do...while loop,
the steps for which are as follows:
Step 1 -
The code block is executed
without any checks at the beginning.
The value of iteration is displayed
and
its value is incremented by 1.
Step 2 -
At the end of the iteration,
the condition iteration < 6 is evaluated.
Since, the current value of iteration is 2,
the condition evaluates to true
and
the loop moves to the next iteration,
wherein it repeats the steps from Step 1.
These steps are repeated
as long as the condition
of the do...while loop
evaluates to true.
In the above example, at one point,
the value of iteration will become 6,
due to which the condition
iteration < 6 will evaluate to false
and
the execution of the loop
will be stopped.
The do...while loop is
similar to the while loop,
with the only difference being that
in the do...while loop,
the loop condition is checked
at end of an iteration,
whereas
in the while loop,
the loop condition is checked
at the start of an iteration.
Due to this behavior,
the code block in a do...while loop
is executed at least once,
as shown in the example below.
In the example above,
we use both while
and
do..while loops.
Both loops have the same condition
and
have the value of iteration as 1
before the beginning of each loops.
However, we only get the output
from the do...while loop.
This is because,
the condition iteration < 1,
evaluates to false from the first iteration.
In the while loop,
since the condition is checked
before the first iteration,
the execution of the loop was stopped
even before the first iteration.
In the do...while loop,
the condition is checked
after the first iteration is complete.
Hence execution of the loop was stopped
after the first iteration
and
"do...while loop"
is displayed at least once.