Object Pascal - Fundamental Operations

	Fundamental Operations

Object Pascal Operators

Introduction to Operations

An operation is an action performed on one or more variables either to modify the value held by one or both of the variables or to produce a new value by combining variables. Therefore, an operation is performed using at least one symbol and one variable. The symbol used in an operation is called an operator. A variable or a value involved in an operation is called an operand.

A unary operator is one that uses only one operand. An operator is referred to as binary if it operates on two operands.

The Assignment Operator

We mentioned in the previous lesson that, when declaring a variable, a space is reserved in the computer memory for that variable. In order to “fill” that space with a value, you must initialize it. Initiazing a variable consists of giving it a recognizable value.

To initialize a variable, use the assignment operator represented as :=. The syntax used is:

VariableName := Value;

The VariableName must be a previously declared variable or one that exists one way or another. The VariableName is followed by the assignment operator := which is followed by the desired value to give to the VariableName. Here is an example:

proggram Greeting;

{$APPTYPE CONSOLE}

var NumberOfPages: Integer;
begin
	NumberOfPages := 812;

	Write('Press any key to continue...');
	Readln;
end.

When initializing a variable, make sure that the value you are giving it respects the type of data the variable was declared with. If the variable was declared as a character, when initializing it, you can include the desired character in single-quotes. Here is an example:

program Greeting;

{$APPTYPE CONSOLE}

var
	NumberOfPages: Integer;
	Gender: AnsiChar;
begin
	NumberOfPages := 812;
	Gender := 'M';

	Write('Press any key to continue...');
	Readln;
end.

If the variable was declared as a string, initialize it with a single typed in single quotes. Here is an example:

program Greeting;

{$APPTYPE CONSOLE}

var
	NumberOfPages: Integer;
	Gender: AnsiChar;
	FullName: AnsiString;
begin
	NumberOfPages := 812;
	Gender := 'M';
	FullName := 'Jean-Jacques Simonet';

	Write('Press any key to continue...');
	Readln;
end.

If the variable was declared as Boolean, initialize it with True or False. Here is an example:

program Greeting;

{$APPTYPE CONSOLE}

var
	NumberOfPages: Integer;
	Gender: AnsiChar;
	FullName: AnsiString;
	IsMarried: Boolean;
begin
	NumberOfPages := 812;
	Gender := 'M';
	FullName := 'Jean-Jacques Simonet';
	IsMarried := False;

	Write('Press any key to continue...');
	Readln;
end.:

The Equality Operator

Object Pascal provides an operator highly used to perform comparisons but it is also used to assign a value to a type. The operator is =. This operator is primarily used to create a type of data as we used it when introducing enumerators. We will also use it with classes, etc.

In the previous lesson, we saw that a constant must be initialized in order to be used. This is taken carer of using the equality operator. Here is an example:

program Greeting;

{$APPTYPE CONSOLE}

const MinimumAge = 18;

begin

	Write('Press any key to continue...');
	Readln;
end.

In the same way, you can create and initialize as many constants as your program needs. Once such a constant has been initialized, it can be accessed by its name. For example, its name can be provided to the Write or the Writeln procedures to display on a console window:

program Greeting;

{$APPTYPE CONSOLE}

const MinimumAge = 18;
const ShipsWithACD = True;
const PI = 3.14159;
const MaxStudents = 42;
const Country = 'New Zealand';
const Distance = 1678212;

begin

	Readln;
end.

Parentheses

Like most computer languages, Object Pascal uses parentheses to isolate a group of items that must be considered as belonging to one entity. For example, as we will learn soon, parentheses allow a function or a procedure to delimit the list of its arguments.

Parentheses can also be used to isolate an operation or an expression with regard to another operation or expression. For example, when studying the algebraic operations, we will see that the subtraction is not associative and can lead to unpredictable results. In the same way, if your operation involves various operators such as addition(s) and subtraction(s), you can use parentheses to tell the compiler how to proceed with the operations, that is, what operation should (must) be performed first. Consider the following algebraic operation:

154 - 12 + 8

The question here is to know whether you want to subtract the addition of 12 and 8 from 154 or you want to add the difference between 154 and 12 to 8. Using parentheses, you can communicate your intentions to the compiler. This is illustrated in the following program:

program Project1;

{$APPTYPE CONSOLE}

begin
	Write('(154 - 12) + 8 = ');
	Writeln((154 - 12) + 8);
	Write(' 154 - (12 + 8) = ');
	Writeln(154 - (12 + 8));

	Writeln('Press any key to continue...');
	Readln;
end.

This would produce:

(154 - 12) + 8 = 150
154 - (12 + 8) = 134
Press any key to continue...

As you can see, using the parentheses controls how the whole operation would proceeds This difference can be even more accentuated if your operation includes 3 or more operators and 4 or more operands.

The Comma

A comma is used in Object Pascal to separate a list of items that come as a group. In the previous lesson, we used commas when creating enumerators and other types of variables. Another way you can use a comma is to separate items to display in a Write or a Writeln procedure. Here is an example:

program Project1;

{$APPTYPE CONSOLE}
var
	Country: string;
	NumberOfPages: Integer;
begin
	Country := 'Sri Lanka';
	NumberOfPages := 812;

	Writeln('Country: ', Country);
	Writeln('Number Of Pages: ', NumberOfPages);

	Write('Press any key to continue...');
	Readln;
end.

This would produce:

Country: Sri Lanka
Number Of Pages: 812
Press any key to continue...

Colons

In the previous lesson, we used the colons when declaring variables. A colon can also be used to format the display of a floating-point number. To do this, type the number or variable followed by a colon. Then, on the right side of the colon, you can type an integer number. Here is an example:

program Colons;

uses
	SysUtils;

{$APPTYPE CONSOLE}

var
	a: Single;
begin
	a := 126.06;
	Write(a:2);

	Readln;
end.

This would produce:

1.2E+0002

When writing a:2, the compiler is asked to provide a minimum space to display the value of a. If you want to control the number of decimal places when displaying the number, add another colon followed by the number of decimal values to the right of the decimal separator. Here is an example:

program Colons;

uses
	SysUtils;

{$APPTYPE CONSOLE}

var
	a: Single;
begin
	a := 126.0684;
	Write(a:4:2);

	Readln;
end.

This would produce:

126.07

Square Brackets

Square brackets are mostly used to control the dimension or index of an array. We will learn how to use them when we study arrays.

Unary Operators

Unary Operators: The Positive Operator +

Algebra uses a type of ruler to classify numbers. This ruler has a middle position of zero. The numbers on the left side of the 0 are considered negative while the numbers on the right side of the 0 are considered positive:

-∞	-6	-5	-4	-3	-2	-1	1	2	3	4	5	6	+∞
0
-∞	-6	-5	-4	-3	-2	-1	1	2	3	4	5	6	+∞

A value on the right side of 0 is considered positive. To express that a number is positive, you can write a + sign on its left. Examples are +4, +228, +90335. In this case the + symbol is called a unary operator because it acts on only one operand.

The positive unary operator, when used, must be positioned on the left side of its operand.

As a mathematical convention, when a value is positive, you do not need to express it with the + operator. Just writing the number without any symbol signifies that the number is positive. Therefore, the numbers +4, +228, and +90335 can be, and are better, expressed as 4, 228, 90335. Because the value does not display a sign, it is referred as unsigned as we learned in the previous lesson.

Unary Operators: The Negative Operator -

As you can see on the above ruler, in order to express any number on the left side of 0, it must be appended with a sign, namely the - symbol. Examples are -12, -448, -32706. A value accompanied by - is referred to as negative.

The negative operator, –, must be typed on the left side of the number it is used to negate.

Remember that if a number does not have a sign, it is considered positive. Therefore, whenever a number is negative, it must have a - sign. In the same way, if you want to change a value from positive to negative, you can just add a - sign to its left.

Here is an example that uses two variables. One has a positive value while the other has a negative value:

program Project1;

{$APPTYPE CONSOLE}
var
	Number1: Integer;
	Number2: Integer;
begin
	Number1 := 802;
	Number2 := -62;

	Writeln('The value of the first number is: ', Number1);
	Writeln('The value of the second number is: ', Number2);

	Write('Press any key to continue...');
	Readln;
end.

This would produce:

The value of the first number is: 802
The value of the second number is: -62
Press any key to continue...


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