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 FOR..NEXT block are visible only inside the block, and can't be accessed outside it.

Differences from QB

- None

See also

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