Pure Programmer
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Constants

Often when we write a program, we need to use the same literal value over and over. Not only is it tedious to key in the same literal over and over, but it is also prone to error. For example if you write a program that uses trigonometry functions, we would often need the value for [[π]] which is approximately 3.141592653589793. You can see how tedious it would be to type this literal value not to mention the likelihood of transposition or other errors. Having a simple named constant symbol such as PI would make writing such a program much easier.

It is also possible that we need to use literal values in our program that change from time-to-time but not during the running of our program. Values like local sales tax rate or the [[cosmological constant]] only change infrequently so having a single place to make the required change when it is necessary helps greatly with program maintenance.

Types

In order to declare named constants or variables, we need to specifically declare what type of value they should hold. This idea is known as strong typing. By declaring the types of our symbols, it helps the compiler to detect problems that might arise from mixing different data types. If, as is the case with constants, we provide an initializer value, the compiler will determine the type of the constant from the initializer so we needn't declare it ourselves. The table below lists the fundamental (or intrinsic) types supported by Swift.

Intrinsic Data Types
TypeKeyword
BooleanBool
CharacterCharacter
8-Bit IntegerInt8
16-Bit IntegerInt16
32-Bit IntegerInt32
64-Bit IntegerInt64
32-Bit Floating PointFloat
64-Bit Floating PointDouble
StringString
VoidVoid

Declaration Syntax

Named constants must be initialized to a specific value when they are declared. Once initialized, they can not have their value changed during the execution of the program. The syntax for a constant declaration consists of the keyword let, the name of the constant (see rules for identifiers), the equal sign (=), the initializer value for the constant and ends at the newline. Examples of statements used to declare a named constants are illustrated below.

let PI = 3.141592653589793
let SALES_TAX_RATE = 0.075
let MAX_COLUMNS = 3
let WELCOME_MESSAGE = "Welcome, welcome!"
Named Constants Example

Questions

  1. What are some examples of integer constants?
  2. What are some examples of floating point constants?
  3. What are some examples of string constants?

Projects

More ★'s indicate higher difficulty level.

References