Do...Loop
Control flow statement for looping
Syntax
`
Do [ { Until | While } condition ]
[ statement block ]
Loop
or
Do
[ statement block ]
Loop [ { Until | While } condition ]
`
Description
The `Do` statement executes the statements in the following `statement block` until/while the `condition`, if any, evaluates to true.
If `Until` is used, the `Do` statement stops repetition of the `statement block` when `condition` evaluates to true. The `While` keyword has opposite effect, stopping the loop if condition evaluates to false. If both `condition` and either `Until` or `While` are omitted, the `Do` statement loops indefinitely.
If an `Exit` `Do` statement is encountered inside the `statement block`, the loop is terminated, and execution resumes immediately following the enclosing `Loop` statement. If a `Continue` `Do` statement is encountered, the rest of the `statement block` is skipped and execution resumes at the `Do` statement.
In the first syntax, the `condition` is checked when the `Do` statement is first encountered, and if the `condition` is met, the `statement block` will be skipped. In the second syntax, `condition` is initially checked after the `statement block` is executed. This means that the `statement block` is always guaranteed to execute at least once.
`condition` may be any valid expression that evaluates to False (zero) or True (non-zero).
Example
In this example, a `Do` loop is used to count the total number of odd numbers from 1 to 10. It will repeat `until` its `n > 10` condition is met:
`
Dim As Integer n = 1 '' number to check
Dim As Integer total_odd = 0 '' running total of odd numbers
Do Until( n > 10 )
If( ( n Mod 2 ) > 0 ) Then total_odd += 1 '' add to total if n is odd (has remainder from division by 2)
n += 1
Loop
Print "total odd numbers: " ; total_odd '' prints '5'
End 0
`
Here, an infinite DO loop is used to count the total number of evens. We place the conditional check inside the loop via an `If...Then` statement, which exits the loop if and when `n > 10` becomes true:
`
Dim As Integer n = 1 '' number to check
Dim As Integer total_even = 0 '' running total of even numbers
Do
If( n > 10 ) Then Exit Do '' exit if we've scanned our 10 numbers
If( ( n Mod 2 ) = 0 ) Then total_even += 1 '' add to total if n is even (no remainder from division by 2)
n += 1
Loop
Print "total even numbers: " ; total_even '' prints '5'
End 0
`
Dialect Differences

- In the -lang qb and -lang fblite dialects, variables declared inside a `Do`..`Loop` block have a function-wide scope as in QB
- In the -lang fb and -lang deprecated dialects, variables declared inside a `Do`..`Loop` block are visible only inside the block, and can't be accessed outside it. To access duplicated symbols defined as global outside this block, add one or preferably two dot(s) as prefix: `.SomeSymbol` or preferably `..SomeSymbol` (or only `..SomeSymbol` if inside a With..End With block).

Differences from QB

- None

See also

- `Continue`
- `Exit`
- `For...Next`
- `While...Wend`