5.2 Primitive values

In this section, we further describe data-items that hold primitive values.

Floating point values

Data-items such as balance and interestRate are examples of data-items holding values of float value types, which represents a subset of the real numbers. These data-items are declared as follows:

balance: var float
interestRate: var float

The set of real numbers is infinite, and a computer can only represent a subset of the real values. This subset is called floating point values. Since only a subset can be represented, the evaluation of floating point expressions often imply that some values are rounded to a value that the computer can represent. For calculations of a large amount of numbers these roundings may lead to misleading and erroneous results. It is therefore recommended that people writing programs involving floating point calculations learn about how to avoid rounding errors.

The specification var float in the declarations of balance and interestRate specifies that these may hold floating point values, and that their type is float.

Examples of float values are: 100, 3.14, 0.56, -12.11, 13.5E7, and 1.11E-7. The 'E' in 13.5E7 means that the value is 13.7 multiplied by 10⁷.

The keyword var used in the declaration specifies that these data-items are variable, which means that they may be assigned different values during the execution of the program:

balance := 500
interestRate := 3.07
...
balance := balance + amount
interestRate := 2.9
...

It is possible to define a float constant using the keyword val:

pi: val 3.14

The default value for a float variable is zero (0.0).

Integer values

In section 3.4 maxNoOfAccounts and noOfAccounts of class Customer are examples of data-items holding integer values.

class Customer(name: var String): 
   addr: var String 
   email: var String
   maxNoOfAccounts: val 10
   noOfAccounts: var integer
   accounts: obj Array(maxNoOfAccounts, Account)

Integer is another example of a primitive value type. Examples of Integer values are 17, 111, -4, 0, and -1014.

As for float, an Integer may be declared as a constant or a variable. In the above example, maxNoOfAccounts is a constant and noOfAccounts is a variable.

The data-item noOfAccounts is an example of a variable that may hold different integers during the program execution, while the data-item maxNoOfAccounts on the other hand is constant. i.e. holding the value 10 during the whole programm execution.

The default value for an integer variable is zero (0).

Boolean values

In section 3.4 the method addAccount of Customer has an if-then-else-statement:

if (noOfAccounts <= maxNoOfAccounts) :then
    accounts.put(acc):at[noOfAccounts]
:else
    console.print(“Cannot add Account”)

The expression noOfAccounts <= maxNoOfAccounts evaluates to one of the values True or False, which both are Boolean values. Boolean is another example of a primitive type and True and False are the only values of type Boolean. We may declare a data-time of type Boolean as follows:

   b1: val True
   b2: var Boolean

The data-item b1 is a constant having the value True during the whole program execution. The data-item b2 is a variable that may hold the values True or False at different points during the program execution. In the next example, b2 is assigned the value False

   b2 := False

We may add a boolean isClosed to class Account to represent whether or not the account is open or closed. An alternative may be to add a closingDate for the account and then make isClosed a method returning a boolean which is true if closingDate <= thisDate and false otherwise.

The default value for a boolean variable is the value false.

Character values

A String consists of characters from some character set like UniCode, Latin1, etc. The type char may be used to declare a data-item holding a value representing a character.

A character may be a letter, a digit, a special character, a blank/space or an end-of-line character. A character literal is typically written within single quotes like:

   ‘a’, ‘b’, ‘Q’, 'L’  — examples of letters
   ‘0’, 7′             — examples of digits
   ‘.’, ‘:’, ‘+’,      — examples of special characters
   ‘ ‘                 — the blank character

An end-of-line character has no graphical form and is thus denoted as ‘\n’. The character ‘\’ is a so-called escape character the implies that the next character defines a special character. The following are examples of characters defined using the escape character

   ‘\n’  — end-of-line
   ‘\t’  — tabulator
   ‘\”   — the quote character ‘
   ...

The following example shows the declaration of data-items of type char and assignment statements:

   ch1: val ‘!’
   ch2: var char
   ch2 := ‘Q’

The data-item ch1 is a a constant holding the exclamation mark character '!'. The data-item ch2 is a variable of type char. It may hold different character values during the program execution. Execution of the assignment statement ch2 := 'Q' has the effect that ch2 holds the character 'Q'. 

So far we have not seen examples using char, but such examples will be shown later in this book, see e.g. section .

The default value for a char variable is the zero char, which is a character that has the integer value zero.