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The Subtraction
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The subtraction operation is used to take out or subtract a value from
another value. It is essentially the opposite of the addition.
The subtraction in Object Pascal is performed with the - symbol. |
program Subtract;
uses
SysUtils;
{$APPTYPE CONSOLE}
// Values used in this program
var
Value1, Value2, Value3: Integer;
begin
// Get the values from the user
Write('Type the first number: ');
Readln(Value1);
Write('Type another number: ');
Readln(Value2);
// Subtract the first value from the second
Value3 := Value1 - Value2;
Writeln;
Writeln(Value1, ' - ', Value2, ' = ', Value3);
Readln;
end.
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The Multiplication
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The multiplication allows adding one value to itself a certain number of
times, set by a second value. As an example, instead of adding a value
to itself in this manner: a + a + a + a, since the variable a is
repeated over and over again, you could simply find out how many times a
is added to itself, then multiply a by that number which, is this case,
is 4. This would mean adding a to itself 4 times, and you would get the
same result.
The multiplication is performed with the * sign which is typed with Shift + 8. Just like the addition, the multiplication is associative: a * b * c = c * b * a. When it comes to programming syntax, the rules we learned with the addition operation also apply to the multiplication. |
program Multiply1;
uses
SysUtils;
{$APPTYPE CONSOLE}
var
a, b: Single;
begin
// Multiple of a and b.
Writeln(' - Type two values -');
Write('First: ');
Readln(a);
Write('Second: ');
Readln(b);
Writeln;
Writeln(a:0:2, ' * ', b:0:2, ' = ', (a * b):0:2);
Write('Press any key to continue...');
Readln;
end.
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The Real Division
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Dividing an item means cutting it in pieces or fractions of a set value.
For example, when you cut an apple in the middle, you are dividing it
in 2 pieces. If you cut each one of the resulting pieces, you will get 4
pieces or fractions. This is considered that you have divided the apple
in 4 parts. Therefore, the division is used to get the fraction of one
number in terms of another.
Object Pascal provides two type of divisions. A division performed on floating-point numbers uses the forward slash / symbol. When performing the division, be aware of its many rules. Never divide by zero (0). Make sure that you know the relationship(s) between the numbers involved in the operation. |
program Division1;
uses
SysUtils;
{$APPTYPE CONSOLE}
var a: Single;
begin
// Get a number from the user.
Write('Type a number: ');
Readln(a);
Writeln;
Writeln('Half of ', a:2:2, ' is ', (a / 2):2:2);
Write('Press any key to continue...');
Readln;
end.
Execute the program to test it. Here is an example:
Type a number: 258.64 Half of 258.64 is 129.32 Press any key to continue...
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Integer Division
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Object Pascal provides another operator to perform a division. This one
applies only to integral values and uses the div operator.
Here is an example: |
program Project1;
{$APPTYPE CONSOLE}
var // Number of students in
Class1, Class2, Class3, Class4, Class5: Integer;
TotalStudents, AvgInClass: Integer;
begin
Class1 := 35;
Class2 := 28;
Class3 := 42;
Class4 := 38;
Class5 := 44;
TotalStudents := Class1 + Class2 + Class3 + Class4 + Class5;
AvgInClass := TotalStudents div 5;
Writeln('Average number of students in a class: ', AvgInClass);
Write('Press any key to continue...');
Readln;
end.
This would produce:
Average number of students in a class: 37 Press any key to continue...
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The Remainder
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The division program above will give you a result of a number with
decimal values if you type an odd number (like 147), which is fine in
some circumstances. Sometimes you will want to get the value remaining
after a division renders a natural result.
The remainder operation is performed using the mod operator. Here is an example: |
program Project1;
{$APPTYPE CONSOLE}
var
Players: Integer;
begin
Players := 16;
// When the game starts, how many players will wait?.
Writeln('Out of ', Players, ' players, ',
26 mod 11, ' players will have to wait when the ',
' football match starts.');
Write('Press any key to continue...');
Readln;
end.
This would produce:
Out of 16 players, 4 players will have to wait when the football match starts. Press any key to continue...
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Incrementing a Number
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We are used to counting numbers such as 1, 2, 3, 4, etc. In reality,
when counting such numbers, we are simply adding 1 to a number in order
to get the next number in the range. Object Pascal provides a technique
of transparently counting such numbers.
The simplest technique of incrementing a value consists of adding 1 to it. After adding 1, the value or the variable is (permanently) modified and the variable would hold the new value. This is illustrated in the following example: |
program Project1;
{$APPTYPE CONSOLE}
var
Value: Integer;
begin
Value := 12;
Writeln('Value = ', Value);
Value := Value + 1;
Writeln('Value = ', Value);
Write('Press any key to continue...');
Readln;
end.
This would produce:
Value = 12 Value = 13
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Decrementing – Pre and Post-Decrementing
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When counting numbers backward, such as 8, 7, 6, 5, etc, we are in fact
subtracting 1 from a value in order to get the lesser value. This
operation is referred to as decrementing a variable. This operation
works as if a variable called Value has its value diminished by 1, as in
Value = Value – 1:
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program Project1;
{$APPTYPE CONSOLE}
var
Value: Integer;
begin
Value := 15;
Writeln('Value = ', Value);
Value := Value - 1;
Writeln('Value = ', Value);
Write('Press any key to continue...');
Readln;
end.
This would produce:
Value = 15 Value = 14 Press any key to continue...
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Variable Casting
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Introduction
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A compiler has the duty of rendering good results, but sometimes it
cannot. It may not be able to figure out what is going on in your
program. This means that, sometimes you have to be explicit. When
performing operations on variables of different types, you need to tell
the compiler what form of result you are expecting. For example, you can
ask the compiler to convert a variable or result from one type to
another, otherwise the compiler might just "make up its own mind". Most
of the time you will not like it.
Value casting consists of converting the type of data that the value is holding into another type.
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Value Casting
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In order to cast a value into another, the new value must be able to fit
into the memory space of the old one. This means that an integer cannot
be cast with a floating-point number.
To cast a value from one type to another, you can use the following syntax: DataType(Expression)
Here is an example:
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program Project1;
{$APPTYPE CONSOLE}
var Value: Integer;
begin
Value := 104;
Writeln(Value, ' cast to a char is ', Char(Value));
Write('Press any key to continue...');
Readln;
end.
This would produce:
104 cast to char is h Press any key to continue...
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Operator Precedence and Direction
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When combining operations in Object Pascal, there are two aspects involved: an operator's precedence and its direction.
If you ask a program to add two numbers, for example 240 + 65, the program will execute the operation by adding 240 to 65. In other words, it would read 240, then +, then 65, and evaluate the result. This is considered as operating from left to right: 240 -> + -> 65. This process is referred to as the direction of the operation. As you will regularly combine operators on your various calculations, each operation is known for how much it "weighs" as compared to other operators. This is known as its precedence. This means that when a certain operator is combined with another, such as a + b * c, or x / y - z, some operators would execute before others, almost regardless of how you write the operation. That's why an operator could be categorized by its level of precedence. Object Pascal categorizes precedence as follows: |
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