Pascal - Constants
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- Category: Chapter 1
- Published: Sunday, 14 April 2013 14:20
- Written by Sternas Stefanos
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A constant is an entity that remains unchanged during program execution. Pascal allows only constants of the following types to be declared:
- Ordinal types
- Set types
- Pointer types (but the only allowed value is Nil).
- Real types
- Char
- String
1. Declaring Constants
Syntax for declaring constants is as follows:
const identifier = constant_value;
The following table provides examples of some valid constant declarations:
Constant Type | Examples |
---|---|
Ordinal(Integer)type constant | valid_age = 21; |
Set type constant | Vowels = set of (A,E,I,O,U); |
Pointer type constant | P = NIL; |
Real type constant | e = 2.7182818; velocity_light = 3.0E+10; |
Character type constant | Operator = '+'; |
String type constant | president = 'Johnny Depp'; |
The following example illustrates the concept:
program const_circle (input,output); const PI =3.141592654; var r, d, c : real; //variable declaration: radius, dia, circumference begin writeln('Enter the radius of the circle'); readln(r); d :=2* r; c := PI * d; writeln('The circumference of the circle is ',c:7:2); end.
When the above code is compiled and executed, it produces following result:
Enter the radius of the circle 23 The circumference of the circle is 144.51
Observe the formatting in the output statement of the program. The variable c is to be formatted with total number of digits 7 and 2 digits after the decimal sign. Pascal allows such output formatting with the numerical variables.