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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
Declaring Constants
Syntax for declaring constants is as follows −
const identifier = constant_value;
The following table provides examples of some valid constant declarations −
| Sr.No | Constant Type & Examples |
|---|---|
| 1 |
Ordinal(Integer)type constant valid_age = 21; |
| 2 |
Set type constant Vowels = set of (A,E,I,O,U); |
| 3 |
Pointer type constant P = NIL; |
| 4 |
e = 2.7182818; velocity_light = 3.0E+10; |
| 5 |
Character type constant Operator = ”+”; |
| 6 |
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 the 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.
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