CHAPTER 14: Blocks and Statements

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14.12 The for Statement

The for statement executes some initialization code, then executes an Expression, a Statement, and some update code repeatedly until the value of the Expression is false .

ForStatement:

	for ( ForInitopt ; Expressionopt ; ForUpdateopt )

		Statement

ForStatementNoShortIf:

	for ( ForInitopt ; Expressionopt ; ForUpdateopt )

		StatementNoShortIf

ForInit:

	StatementExpressionList

	LocalVariableDeclaration

ForUpdate:

	StatementExpressionList

StatementExpressionList:

	StatementExpression

	StatementExpressionList , StatementExpression

The Expression must have type boolean , or a compile-time error occurs.

14.12.1 Initialization

A for statement is executed by first executing the ForInit code:

• If the ForInit code is a list of statement expressions (S14.7), the expressions are evaluated in sequence from left to right; their values, if any, are discarded. If evaluation of any expression completes abruptly for some reason, the for statement completes abruptly for the same reason; any ForInit statement expressions to the right of the one that completed abruptly are not evaluated.
• If the ForInit code is a local variable declaration, it is executed as if it were a local variable declaration statement (S14.3) appearing in a block. In this case, the scope of a declared local variable is its own initializer and any further declarators in the ForInit part, plus the Expression, ForUpdate, and contained Statement of the for statement. If execution of the local variable declaration completes abruptly for any reason, the for statement completes abruptly for the same reason.
• If the ForInit part is not present, no action is taken.

14.12.2 Iteration

Next, a for iteration step is performed, as follows:

• If the Expression is present, it is evaluated, and if evaluation of the Expression completes abruptly, the for statement completes abruptly for the same reason. Otherwise, there is then a choice based on the presence or absence of the Expression and the resulting value if the Expression is present:
  • If the Expression is not present, or it is present and the value resulting from its evaluation is true , then the contained Statement is executed. Then there is a choice:
    • If execution of the Statement completes normally, then the following two steps are performed in sequence:
      • First, if the ForUpdate part is present, the expressions are evaluated in sequence from left to right; their values, if any, are discarded. If evaluation of any expression completes abruptly for some reason, the for statement completes abruptly for the same reason; any ForUpdate statement expressions to the right of the one that completed abruptly are not evaluated. If the ForUpdate part is not present, no action is taken.
      • Second, another for iteration step is performed.
    • If execution of the Statement completes abruptly, see S14.12.3 below.
  • If the Expression is present and the value resulting from its evaluation is false , no further action is taken and the for statement completes normally.

If the value of the Expression is false the first time it is evaluated, then the Statement is not executed.

If the Expression is not present, then the only way a for statement can complete normally is by use of a break statement.

14.12.3 Abrupt Completion

Abrupt completion of the contained Statement is handled in the following manner:

• If execution of the Statement completes abruptly because of a break with no label, no further action is taken and the for statement completes normally.
• If execution of the Statement completes abruptly because of a continue with no label, then the following two steps are performed in sequence:
  • First, if the ForUpdate part is present, the expressions are evaluated in sequence from left to right; their values, if any, are discarded. If the ForUpdate part is not present, no action is taken.
  • Second, another for iteration step is performed.
• If execution of the Statement completes abruptly because of a continue with label L, then there is a choice:
  • If the for statement has label L, then the following two steps are performed in sequence:
    • First, if the ForUpdate part is present, the expressions are evaluated in sequence from left to right; their values, if any, are discarded. If the ForUpdate is not present, no action is taken.
    • Second, another for iteration step is performed.
  • If the for statement does not have label L, the for statement completes abruptly because of a continue with label L.
• If execution of the Statement completes abruptly for any other reason, the for statement completes abruptly for the same reason. Note that the case of abrupt completion because of a break with a label is handled by the general rule for labeled statements (S14.6).