While
Control flow statement for looping
While [condition]
The While statement will cause the following set of statements in the statement block to execute repeatedly if and while the expression condition evaluates to true.
If condition evaluates to false when the WHILE statement is first executed, then the statement block is skipped and execution resumes immediately following the enclosing Wend statement.
If an Exit While statement is encountered inside the statement block, the loop is terminated, and execution resumes immediately following the enclosing Wend statement. If a Continue While statement is encountered, the rest of the statement block is skipped and execution resumes at the While statement.
Like all control flow statements, the While statement can be nested, that is, it can be used in a statement block of another While statement.
note: the While keyword is also used in the Do...Loop statement to indicate the type of comparison. Used in this way, the DO statement becomes functionally equivalent to the WHILE statement, so do not confuse their enclosing keywords Loop and Wend, respectively.
In this example, a While loop is used to reverse a string by iterating through it backward. The loop stops if index is less than 0 (0 being the first index in the string).
Syntax
While [condition]
[statement block]
WendDescription
The While statement will cause the following set of statements in the statement block to execute repeatedly if and while the expression condition evaluates to true.
If condition evaluates to false when the WHILE statement is first executed, then the statement block is skipped and execution resumes immediately following the enclosing Wend statement.
If an Exit While statement is encountered inside the statement block, the loop is terminated, and execution resumes immediately following the enclosing Wend statement. If a Continue While statement is encountered, the rest of the statement block is skipped and execution resumes at the While statement.
Like all control flow statements, the While statement can be nested, that is, it can be used in a statement block of another While statement.
note: the While keyword is also used in the Do...Loop statement to indicate the type of comparison. Used in this way, the DO statement becomes functionally equivalent to the WHILE statement, so do not confuse their enclosing keywords Loop and Wend, respectively.
Example
In this example, a While loop is used to reverse a string by iterating through it backward. The loop stops if index is less than 0 (0 being the first index in the string).
Dim As String sentence '' string to reverse
sentence = "The quick brown fox jumps over the lazy dog."
Dim As String ecnetnes
Dim As Integer index
index = Len( sentence ) - 1 '' point to last character
While( index >= 0 ) '' stop after first character
ecnetnes += Chr( sentence[index] ) '' append character to new string
index -= 1
Wend
Print "original: """ ; sentence ; """"
Print "reversed: """ ; ecnetnes ; """"
End 0
sentence = "The quick brown fox jumps over the lazy dog."
Dim As String ecnetnes
Dim As Integer index
index = Len( sentence ) - 1 '' point to last character
While( index >= 0 ) '' stop after first character
ecnetnes += Chr( sentence[index] ) '' append character to new string
index -= 1
Wend
Print "original: """ ; sentence ; """"
Print "reversed: """ ; ecnetnes ; """"
End 0
Dialect Differences
- In the -lang qb and -lang fblite dialects, variables declared inside a WHILE..WEND loop have a function-wide scope as in QB
- In the -lang fb and -lang deprecated dialects, variables declared inside a While..Wend block are visible only inside the block, and can't be accessed outside it.
Differences from QB
- None
See also
