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5.3 If Statements

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1

[An if_statement selects for execution at most one of the enclosed sequences_of_statements, depending on the (truth) value of one or more corresponding conditions.]

Syntax​

2 
if_statement ::= 
    if condition then
      sequence_of_statements
   {elsif condition then
      sequence_of_statements}
   [else
      sequence_of_statements]
    end if;

Paragraphs 3 and 4 were deleted.

Dynamic Semantics​

5/3

For the execution of an if_statement, the condition specified after if, and any conditions specified after elsif, are evaluated in succession (treating a final else as elsif True then), until one evaluates to True or all conditions are evaluated and yield False. If a condition evaluates to True, then the corresponding sequence_of_statements is executed; otherwise, none of them is executed.

5.a
ramification

The part about all evaluating to False can't happen if there is an else, since that is herein considered equivalent to elsif True then.

Examples​

6

Examples of if statements:

7 
if Month = December and Day = 31 then
   Month := January;
   Day   := 1;
   Year  := Year + 1;
end if;

8
if Line_Too_Short then
   raise Layout_Error;
elsif Line_Full then
   New_Line;
   Put(Item);
else
   Put(Item);
end if;

9
if My_Car.Owner.Vehicle /= My_Car then            -- see 3.10.1
   Report ("Incorrect data");
end if;

Wording Changes from Ada 2005​

9.a/3

Moved definition of condition to 4.5.7 in order to eliminate a forward reference.