DO

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Purpose

The DO statement controls the execution of the statements that follow it, up to and including a specified terminal statement. Together, these statements form a DO construct.

Syntax

Read syntax diagramSkip visual syntax diagramDO_construct_name:DOstmt_label,var_name =  a_expr1,  a_expr2 ,  a_expr3
DO_construct_name
is a name that identifies the DO construct.
stmt_label
is the statement label of an executable statement appearing after the DO statement in the same scoping unit. This statement denotes the end of the DO construct.
var_name
is a scalar variable name of type integer or real, called the DO variable
a_expr1, a_expr2, and a_expr3
are each scalar expressions of type integer or real

Rules

If you specify a DO_construct_name on the DO statement, you must terminate the construct with an END DO and the same DO_construct_name. Conversely, if you do not specify a DO_construct_name on the DO statement, and you terminate the DO construct with an END DO statement, you must not have a DO_construct_name on the END DO statement.

If you specify a statement label in the DO statement, you must terminate the DO construct with a statement that is labeled with that statement label. You can terminate a labeled DO statement with an END DO statement that is labeled with that statement label, but you cannot terminate it with an unlabeled END DO statement. If you do not specify a label in the DO statement, you must terminate the DO construct with an END DO statement.

If the control clause (the clause beginning with var_name) is absent, the statement is an infinite DO. The loop will iterate indefinitely until interrupted (for example, by the EXIT statement).

Examples

INTEGER :: SUM=0
OUTER: DO
  INNER: DO M=1,10
    READ (5,*) J
    IF (J.LE.I) THEN
      PRINT *, 'VALUE MUST BE GREATER THAN ', I
      CYCLE INNER
    END IF
    SUM=SUM+J
    IF (SUM.GT.500) EXIT OUTER
    IF (SUM.GT.100) EXIT INNER
  END DO INNER
  SUM=SUM+I
  I=I+10
END DO OUTER
PRINT *, 'SUM =',SUM
END

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