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Do Loops (Basic Syntax)

Visual Studio .NET 2003

A Do loop can be used to execute a fixed block of statement an indefinite number of times.

The 4 different types of Do loops

Type of Do Loop Explanation Example
Do While Loop The Do While ... Loop evaluates the condition, and if the condition is true, then it evaluates the statements following the condition.

When it has finished doing this, it evaluates the condition again and if the condition is true, it evaluates the statements again.

It continues repeating this process until the condition is false.

Do While condition
   statements
Loop

Do Until ... Loop The Do Until ... Loop is similar to the Do While ... Loop except it keeps evaluating the statements until the condition is true rather than while it is true.
Do Until condition
   statements
Loop

Do ... Loop While The Do ... Loop While evaluates the statements only once.

It then evaluates the condition, and if the condition is true, evaluates the statements again. This process continues until the condition is false.

Do
   statements
Loop While condition

Do ... Loop Until Similar to Do ... Loop While except that it evaluates the statements until the condition is true.
Do
   statements
Loop Until condition

Note   The Do loops support an Exit Do statement to immediately jump out of the loop. The Exit Do statement is similar to the Exit For in For/Next loops.

Do While ... Loop Formula Example

The following example searches for the first occurrence of a digit in an input string. If a digit is found, it returns its position, otherwise it returns -1. In this case, the input string is set explicitly to a string constant, but it could be set equal to a String type database field instead.

For example, for the input String, "The 7 Dwarves", the formula returns 5, which is the position of the digit 7.

Dim inString
inString = "The 7 Dwarves"
Dim i, strLen
i = 1
strLen = Len (inString)
formula = -1
Do While i <= strLen And formula = -1
   Dim c As String
   c = Mid (inString, i, 1)
   If IsNumeric (c) Then formula = i
   i = i + 1
Loop

See Also

While Loops

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