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Operators & Identifiers

Operators & Identifiers. The Data Elements. exponentiation multiplication division ( real ) division ( integer quotient ) division ( integer remainder ) addition Subtraction assignment. ^ * / Mod + - =. Arithmetic Operators. Evaluate these expressions.

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Operators & Identifiers

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  1. Operators & Identifiers The Data Elements

  2. exponentiation multiplication division (real) division (integer quotient) division (integer remainder) addition Subtraction assignment ^ * / \ Mod + - = Arithmetic Operators

  3. Evaluate these expressions

  4. Evaluate these expressions

  5. Evaluate these expressions

  6. Evaluate these expressions

  7. Evaluate these expressions

  8. Evaluate these expressions

  9. 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.

  10. Some VB Data Types

  11. Identifiers There are two types of identifiers for scalar data: • Constants • Variables

  12. 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

  13. Constants Note that the type declaration can be omitted for brevity. Const g = 9.8 VB will use the data to determine type.

  14. 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

  15. 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

  16. Exploring Integer Data Types

  17. 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

  18. 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 1 32768+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?

  19. 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?

  20. 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

  21. 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

  22. Data Type Conversion

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