Program Control Statements

Developer Guide and Reference

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Date 10/31/2024

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Program Control Statements

The following table lists statements that affect program control.

Unless identified as an image control statement, the statement affects execution on a single image. With the exception of STOP, ERROR STOP, and END PROGRAM, image control statements are used with coarrays; they involve synchronization of images and they divide the program into segments.

Name	Description
ALLOCATE ^¹	Allocates a coarray.
BLOCK ^²	Identifies a block of code. It can contain declarations of entities that are local to the block.
CALL	Transfers control to a subroutine.
CALL MOVE_ALLOC ^¹	Relocates a coarray in memory.
CASE	Within a SELECT CASE construct, marks a block of statements that are executed if an associated value matches the SELECT CASE expression.
CASE DEFAULT or CLASS DEFAULT	Identifies the block of statements to be executed in a SELECT CASE construct if the value of the expression does not match any of the CASE selectors, or in a SELECT TYPE construct if the dynamic type of the selector does not match the type of any of the TYPE IS or CLASS IS statements.
CHANGE TEAM ^³	Causes images of the current team to begin execution on sibling (sub) teams as specified by a team variable created by a FORM_TEAM statement previous executed by the team encountering the CHANGE_TEAM statement.
CLASS IS	Within a SELECT TYPE construct, marks a block of statements that are executed if the type or dynamic type of an expression matches the type of the CLASS IS expression.
CONTINUE	Often used as the target of GOTO or as the terminal statement in a DO loop; performs no operation.
CRITICAL ^³	Begins a critical construct. Only one image can execute the block of statements in the construct at a time.
CYCLE	Advances control to the end statement of a DO loop; the intervening loop statements are not executed.
DEALLOCATE ^¹	Deallocates a coarray.
DO	Marks the beginning of a loop construct. Statements through and including the ending statement may be executed repeatedly.
DO CONCURRENT	Marks the beginning of a DO CONCURRENT construct. The order of executions of iterations of a DO CONCURRENT construct are indeterminate.
DO WHILE	Evaluates statements in the DO WHILE loop, through and including the ending statement, until a logical condition becomes .FALSE..
ELSE	Marks an optional branch in an IF construct.
ELSE IF	Marks an optional branch in an IF construct.
ELSEWHERE	Marks an optional branch in a WHERE construct.
END [PROGRAM]^³	Marks the end the main program. When executed, it initiates normal termination for the image that executes it.
END [FUNCTION] \| [MODULE] \| [SUBROUTINE]^⁴	Marks the end of a program unit.
END BLOCK ^⁴	Terminates a block construct.
END CRITICAL ^³	Terminates a critical construct.
END DO	Marks the end of a series of statements in a DO, DO CONCURRENT, or DO WHILE construct.
END FORALL	Marks the end of a series of statements following a block FORALL statement.
END IF	Marks the end of a series of statements following a block IF statement.
END SELECT	Marks the end of a SELECT CASE, SELECT RANK, or SELECT TYPE statement.
END TEAM ^³	Changes the current team to the parent team of the team of images that executes the END TEAM statement.
END WHERE	Marks the end of a series of statements following a block WHERE statement.
ERROR STOP ^³	Initiates error termination for all images.
EVENT POST ^³	Increments the count of an event variable by one.
EVENT WAIT ^³	Tells the image executing this statement to wait until an event has been posted and to decrement the count of the event variable.
EXIT	Terminates execution of a DO loop or other construct. Execution continues with the first statement that follows the construct.
FAIL_IMAGE	Causes the image that executes it to execute no more statements and stop participating in program execution.
FORALL	Indicates a loop construct where the output from one iteration cannot change the input to another.
FORM TEAM ^³	Creates one or more subteams of the images in the current team and assigns a value describing the teams to a variable of type TEAM_TYPE, which is defined in the intrinsic module ISO_FORTRAN_ENV.
GOTO	Transfers control to a specified part of the program.
IF	Controls conditional execution of other statements.
LOCK ^³	Acquires a LOCK_TYPE variable, preventing other images from acquiring it until it has been unlocked by the image that locked it.
PAUSE	Suspends program execution and, optionally, executes operating-system commands.
RANK	Within a SELECT RANK construct, marks a block of statements that are executed if the rank of an assumed rank array matches the RANK selector.
RANK DEFAULT	Identifies the block of statements to be executed in a SELECT RANK construct if the rank of the array does not match any of the RANK selectors.
RETURN ^⁴	Returns control to the program unit that called a subroutine or function.
SELECT CASE	Transfers program control to a block of statements, determined by the value of an expression.
SELECT RANK	Transfers the program to a block of statements, determined by the rank of an assumed rank array.
SELECT TYPE	Transfers the program to a block of statements, determined by the dynamic type of an expression.
STOP ^³	Initiates normal termination for the image that executes the statement.
SYNC ALL ^³	Synchronizes all of the images of the current team.
SYNC IMAGES ^³	Synchronizes an image with all of the specified images in the image set.
SYNC MEMORY ^³	Ends a segment and begins another; the two segments may be ordered in a user defined manner with respects to segments on other images.
SYNC TEAM ^³	Synchronizes all images on a specified team.
TYPE IS	Within a SELECT TYPE construct, marks a block of statements that are executed if the type or dynamic type of an expression matches the type of the TYPE IS expression.
UNLOCK ^³	Unlocks a variable of type LOCK_TYPE.
WHERE	Controls conditional execution of array assignments and elemental function calls.
¹ This is an image control statement only if it involves a coarray; otherwise, it's not a program control statement. ² This is an image control statement only if the block declares a non-allocatable, non-SAVEd coarray. ³ This is an image control statement ⁴ This is an image control statement only if it involves implicit deallocation of a coarray.

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Program Control Statements