Welcome to the Harris Geospatial product documentation center. Here you will find reference guides, help documents, and product libraries.


Harris Geospatial / Docs Center / IDL Reference / Statements / REPEAT...UNTIL

REPEAT...UNTIL

REPEAT...UNTIL

REPEAT...UNTIL loops are used to repetitively execute a subject statement until a condition is true. The condition is checked after the subject statement is executed. Therefore, the subject statement is always executed at least once. See Definition of True and False for details on how the “truth” of an expression is determined.

Syntax


REPEAT statement UNTIL expression

or

REPEAT BEGIN

   statements

ENDREP UNTIL expression

Examples


The following example finds the smallest power of 2 that is greater than B:

A = 1
B = 10
REPEAT A = A * 2 UNTIL A GT B

The subject statement can also be in the form of a block:

A = 1
B = 10
REPEAT BEGIN
   A = A * 2 
ENDREP UNTIL A GT B

 

The next example sorts the elements of ARR using the inefficient bubble sort method.

;Sort array.
REPEAT BEGIN
   ;Set flag to true.
   NOSWAP = 1
   FOR I = 0, N - 2 DO IF arr[I] GT arr[I + 1]THEN BEGIN
     ;Swapped elements, clear flag.
     NOSWAP = 0
     T = arr[I] & arr[I] = arr[I + 1] & arr[I + 1] = T
     ENDIF
;Keep going until nothing is moved.
ENDREP UNTIL NOSWAP

Tip: A more efficient way to sort elements is to use the SORT function.

Version History


Original

Introduced

See Also


BEGIN...END, BREAK, CASE, CONTINUE, FOR, FOREACH, GOTO, IF...THEN...ELSE, SWITCH, WHILE...DO

IDL Programming



© 2017 Exelis Visual Information Solutions, Inc. |  Legal
My Account    |    Buy    |    Contact Us