5.3 If Statements

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;
   

3. condition ::= boolean_expression
   

   Name Resolution Rules
   
4. A condition is expected to be of any boolean type.
   Dynamic Semantics
   
5. 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.
   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 section 3.10.1 Incomplete Type Declarations
      Report ("Incorrect data");
   end if;
   

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