Operators & Identifiers

The Data Elements

Arithmetic Operators

• exponentiation• multiplication• division (real)• division (integer quotient)• division (integer remainder) • addition• Subtraction• assignment

^

*

/

\

Mod

+

-

=

Evaluate these expressions

= 100 / 10 / 5

= 100 / 10 \ 5

= 100 \ 10 / 5

= 100 + 10 Mod 5

= 100 + 10 \ 5

Evaluate these expressions

= 100 / 10 / 5 2

= 100 / 10 \ 5

= 100 \ 10 / 5

= 100 + 10 Mod 5

= 100 + 10 \ 5

Evaluate these expressions

= 100 / 10 / 5 2

= 100 / 10 \ 5 2

= 100 \ 10 / 5

= 100 + 10 Mod 5

= 100 + 10 \ 5

Evaluate these expressions

= 100 / 10 / 5 2

= 100 / 10 \ 5 2

= 100 \ 10 / 5 50

= 100 + 10 Mod 5

= 100 + 10 \ 5

Evaluate these expressions

= 100 / 10 / 5 2

= 100 / 10 \ 5 2

= 100 \ 10 / 5 50

= 100 + 10 Mod 5 100

= 100 + 10 \ 5

Evaluate these expressions

= 100 / 10 / 5 2

= 100 / 10 \ 5 2

= 100 \ 10 / 5 50

= 100 + 10 Mod 5 100

= 100 + 10 \ 5 102

Identifiers

• An identifier is a string used to identify an area in memory.

• Typically, variable names need to be declared so the operating system can allocate sufficient space.

• The amount of memory is determined by the type of data that it will store.

Some VB Data Types

Boolean 2 bytes True or False (1 or 0)

Char 2 bytes 0 to 65,535 representing the Unicode character set

Date 8 bytes 0:00:00 on 1/1/0001 to 23:59:59 on 31/12/9999

Decimal 16 bytes +/- 79,228,162,514,264,337,593,543,950,335

+/- 7.9228162514264337593543950335

Double 8 bytes +/-4.94065645841247 X 10-324 to

+/-1.79769313486231 X10308

Integer 4 bytes -2,147,483,648 to 2,147,483,647

Long 8 bytes -9,223,382,036,854,775,808 to

9,223,382,036,854,775,807

Object 4 bytes any type

Short 2 bytes -32,768 to 32,767

Single 4 bytes +/- 1.401298 X 10-45 to +/- 3.402823 X 1038

String 0 to approximately 2 billion characters

Identifiers

There are two types of identifiers for scalar data:

•Constants

•Variables

Constants

A constant is a name for a fixed value.

The value of a constant cannot be changed.

They must be declared and initialised in the same step:

Const g As Decimal = 9.8

Constants

Note that the type declaration can be omitted for brevity.

Const g = 9.8

VB will use the data to determine type.

Identifier Names in VB

• Must begin with a letter– Can include letters and numerals– Cannot include spaces

• Use names that are descriptive

• Capitalising convention– InterestRate, InitialCapital

The Scope of Variables

• Local (procedure-level)– Declared within a subprogram– Dim varName As dataType

• Global (module-level)– Declared at the top of the code listing– Private varName As dataType

Exploring Integer Data Types

Short type (low-order byte)

27 26 25 24 23 22 21 20

128 64 32 16 8 4 2 1

1 1 1 1 1 1 1 1

128 +64 +32 +16 +8 +4 + 2 + 1

=255

Short type (high-order byte)

215 214 213 212 211 210 29 28

32768 16384 8192 4096 2048 1024 512 256 1 1 1 1 1 1 1 132768+16384 +8192 +4096 +2048 +1024 +512 +256

=65280 +255 65535

The largest Unsigned value that can be stored in 16 bits.

How many patterns are there?

Short Type

• To store integers, half the combinations are used to represent negative values.

• The range for Integer type variables is:-32,768 to +32767

• The MSB is used to represent the sign.

• Which value of the sign bit (0 or 1) will represent a negative number?

Integer Storage (4 bytes)

• High order bit (MSB) is worth 231

• The number of different combinations= 232

=4,294,967,296

• Half are used for negative values, so the range is– 2,147,483,648 to + 2,147,483,647

Long Integers

• In 8 bytes there are 64 bits!

• High order bit (MSB) is worth 263.

• The number of different combinations

=264

=18,446,744,073,709,650,616

• Ranging from -9,223,382,036,854,775,808to 9,223,382,036,854,775,807

Data Type ConversionFunction Return Type Argument

CBool boolean any valid String or numeric expression

CCur currency a string or numeric expression within the range of currency values

CDbl double real number a string or numeric expression within the range of double real values

CInt integer a string or numeric expression within the range of integer values, fractions are rounded

CLng long integer a string or numeric expression within the range of long integer values, fractions are rounded

CSng single real number a string or numeric expression within the range of single real values

CStr string any valid value or expression

CDate date any value that can be interpreted as a date