Constant is a data whose value cannot be changed during the runtime. Using a constant in a program consumes no RAM memory. Constants can be used in any expression, but cannot be assigned a new value.

Constants are declared in the declaration part of a program or routine. You can declare any number of constants after the keyword const:

const constant_name [: type] = value;

Every constant is declared under unique constant_name which must be a valid identifier. It is a tradition to write constant names in uppercase. Constant requires you to specify value, which is a literal appropriate for the given type. type is optional and in the absence of type, the compiler assumes the “smallest” of all types that can accommodate value.

  Note : You cannot omit type when declaring a constant array.

Pascal allows shorthand syntax with only one keyword const followed by multiple constant declarations. Here’s an example:

const
  MAX : longint = 10000;
  MIN = 1000;      // compiler will assume word type
  SWITCH = 'n';    // compiler will assume char type
  MSG = 'Hello';   // compiler will assume string type
  MONTHS : array[1..12] of byte = (31,28,31,30,31,30,31,31,30,31,30,31);

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