Do...Loop statement - MapBasic - 2023

Purpose

Defines a loop which will execute until a specified condition becomes TRUE (or FALSE).

Restrictions

You cannot issue a Do Loop statement through the MapBasic window.

Syntax 1

Do 
	statement_list 
	Loop [ { Until | While } condition ]

Syntax 2

Do [ { Until | While } condition ] 
	statement_list 
	Loop

statement_list is a group of statements to be executed zero or more times.

condition is a conditional expression which controls when the loop terminates.

Description

The Do...Loop statement provides loop control. Generally speaking, the Do...Loop repeatedly executes the statements in a statement_list as long as a While condition remains TRUE (or, conversely, the loop repeatedly executes the statement_list until the Until condition becomes TRUE).

If the Do...Loop does not contain the optional Until / While clause, the loop will repeat indefinitely. In such a case, a flow control statement, such as Goto statement or Exit Do statement, will be needed to halt or exit the loop. The Exit Do statement halts any Do...Loop immediately (regardless of whether the loop has an Until / While clause), and resumes program execution with the first statement following the Loop clause.

As indicated above, the optional Until / While clause may either follow the Do keyword or the Loop keyword. The position of the Until / While clause dictates whether MapBasic tests the condition before or after executing the statement_list. This is of particular importance during the first iteration of the loop. A loop using the following syntax:

Do
	statement_list 
	Loop While condition 

will execute the statement_list and then test the condition. If the condition is TRUE, MapBasic will continue to execute the statement_list until the condition becomes FALSE. Thus, a Do...Loop using the above syntax will execute the statement_list at least once.

By contrast, a Do...Loop of the following form will only execute the statement_list if the condition is TRUE.

Do While condition 
	statement_list 
	Loop 

Example

The following example uses a Do...Loop statement to read the first ten records of a table.

Dim sum As Float, counter As Integer
Open Table "world"
Fetch First From world
counter = 1
Do
	sum = sum + world.population										 
	Fetch Next From world								 
	counter = counter + 1								 
Loop While counter <= 10 

See Also:

Exit Do statement, For...Next statement