Pascal - Booleans

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Category: Chapter 3
Published: Sunday, 14 April 2013 16:22
Written by Sternas Stefanos
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Pascal provides data types Boolean that enables the programmers to define, store and manipulate logical entities, such as constants, variables, functions and expressions etc.

Boolean values are basically integer type. Boolean type variables have two pre-defined possible values True and False. The expressions resolving to a Boolean value can also be assigned to a Boolean type.

Free Pascal also supports the ByteBool, WordBool and LongBool types. These are of type Byte, Word or Longint respectively.

The value False is equivalent to 0 (zero) and any nonzero value is considered True when converting to a Boolean value. A Boolean value of True is converted to -1 in case it is assigned to a variable of type LongBool.

It shuold be noted that logical operators and, or and not are defined for Boolean data types.

 

1. Declaration of Boolean Data Types

A variable of Boolean type is declared using the var keyword.

varboolean-identifier:boolean;
 

for example,

var
choice:boolean;
 

 

2. Example:

program exBoolean;
var exit:boolean;
    choice: char;
 begin
   writeln('Do you want to continue? ');
   writeln('Enter Y/y for yes, and N/n for no');
   readln(choice);if(choice ='n')then
   exit:=trueelse
  exit:=false;
 if(exit)then
  writeln(' Good Bye!') else
  writeln('Please Continue');
 
 readln;
end.
 

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

Do you want to continue?
Enter Y/y for yes, and N/n for no
N
Good Bye!
Y
Please Continue