Do-loops are useful when you always want to run a codeblock at least once. A Do-loop will evaluate the condition after executing the codeblock, unlike a while-loop which does it before executing the codeblock.
You can use do-loops in two ways:
Do {
code_block
} while (condition)
Do {
code_block
} until (condition)
Real Examples:
$i = 0
Do {
$i++
"Number $i"
} while ($i -ne 3)
Do {
$i++
"Number $i"
} until ($i -eq 3)
Do-While and Do-Until are antonymous loops. If the code inside the same, the condition will be reversed. The example above illustrates this behaviour.