Pascal - Constants

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 vapd constant declarations −

Real type constant

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.