5. Condition processing in Pascal

There is another type of variable in pascal called boolean. It can have only two values, true or false. A statement which results in a true or false value is a boolean expression. ex: n = 8 results in a true value for the expression if n equalto 8. Note the equalto (=) sign in the expression which is different from assignment sign(:=).

Pascal provides language structures to control conditional processing. They are as follows:

1. if --condition-- then --statement1-- else --statement2--;
condition could be a = 10 or boolean. Notice the equal(=) sign in the condition.
Statement1 may not have ';' at the end, if it is followed by else. If it has results could be what you do not expect.

2. while --condition-- do --statement;
As long as the While condition is satisfied the statement processing continues. As such the condition should be changed in the statement otherwise the processing continues for ever.

3. Repeat ---- statements ---- until ---- boolean expression ----;
As noted in While the boolean expression value should change sometime or other, otherwise processing continues for ever.

4. Case --variable-- of --vales of variable-- : statement1; otherwise statement2; end;
ex: case n of 2,3,6 : writeln('value of n is ', n); otherwise writeln('end of case'); end;
For values of n equal to 2,3 or 6 write (value of n is) otherwise write (end of case).

Program depicting the conditional statements follows:

Program program5;
{ Author: Rao S Lakkaraju }
{ This is my fifth pascal program }
(* Condition Processing in Pascal *)

uses crt,graph;
var n,number1, number2,number3 : integer;
interest1, interest2,interest3 : real;
name1, name2, name3 : string;
rich : boolean;

begin
clrscr;
number1 := 1;
number2 := 10;
interest1 := 2.5;
interest2 := 5.4;
name1 := 'Rao';
name2 := ' Lakkaraju';

(**** Lesson 4 *****)
for number3 := number1 to number2 do write(number3);
write(' ');
for number3 := number2 downto number1 do begin write(number3); end;
writeln(' ');
name3 := name1 + name2;
interest3 := interest1 + interest2;
Writeln('number1 = ', number1);
writeln('number2 = ', number2);
writeln('number3 = ', number3);
writeln('interest1 = ', interest1, ' interest2 = ', interest2);
writeln('interest3 = ', interest3);
writeln('My Name is ', name3);

(**** Lesson 5 *****)
rich := false;
if not rich then writeln('I am not rich ')
else writeln('I am rich');
while rich = false do rich := true;
n := 1;
repeat n := n + 1; Writeln('I am in repeat'); until n = 8;
n := 2;
case n of 2,3,6 : writeln('value of n is ', n);
otherwise writeln('end of case'); end;

writeln('My fifth Pascal Program');
readln;
end.

Summary: Pascal provides a variable called boolean which could have only two values true or false. A boolean expression is one which after evaluation results in a boolean true or false value . Pascal provides statement execution depending on the value of a boolean expression. These pascal structures are if, while, repeat and case.