- Details
- Category: Chapter 2
- Published: Sunday, 14 April 2013 14:27
- Written by Sternas Stefanos
- Hits: 19092

It is always legal in Pascal programming to nest **if-else** statements, which means you can use one **if** or **else if** statement inside another **if** or **else if** statement(s). Pascal allows nesting to any level, however, if depends on Pascal implementation on a particular system.

The syntax for a nested if statement is as follows:

if( boolean_expression 1)then if(boolean_expression 2)then S1 else S2;

You can nest else if-then-else in the similar way as you have nested if-then statement. Please note that, the nested **if-then-else** constructs gives rise to some ambiguity as to which else statement pairs with which if statement. *The rule is that the else keyword matches the first if keyword (searching backwards) not already matched by an else keyword.*

The above syntax is equivalent to

if( boolean_expression 1)then begin if(boolean_expression 2) then S1 else S2; end;

It is not equivalent to

if( boolean_expression 1)then begin if exp2 then S1 end; else S2;

Therefore if the situation demands the later construct, then you must put **begin** and **end** keywords at the right place.

program nested_ifelseChecking; var {local variable definition } a, b : integer; begin a :=100; b:=200; (* check the boolean condition *) if(a =100)then (*if condition istruethen check the following *) if( b =200)then (*if nested if condition istrue thenprint the following *) writeln('Value of a is 100 and value of b is 200'); writeln('Exact value of a is: ', a ); writeln('Exact value of b is: ', b ); end.

When the above code is compiled and executed, it produces following result:

Value of a is 100 and b is 200 Exact value of a is : 100 Exact value of b is : 200