Lecture Learning programming using Visual Basic Net – Chapter 4 Performing calculations and manipulating data Expressions

CHAPTER FOUR
Performing Calculations and
Manipulating Data: Expressions


4- 2

Expressions
• Arithmetic expressions
– To perform arithmetic operations.

• String expressions
– To manipulate string data.

• Logical expressions
– To select an appropriate action.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.


4- 3

Objectives
• Describe the operators and functions used to
create arithmetic, string, and logical expressions.
• Explain why errors occur and how to avoid them.
• Write logical expressions using comparison
operators and logical operators.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.


4.1 Using Expressions, Operators, and
Functions in Visual Basic .NET Statements

4- 4

• An expression tells the computer to manipulate
data.
• The statement tells the computer what to do with
the results of an expression.
• Expressions are composed of values, operators,
and functions.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.


4.1 Using Expressions, Operators, and
Functions in Visual Basic .NET Statements
(cont.)

• Statements

– Perform various tasks
• Evaluate expressions one at a time.
• Carry out tasks specified in expressions.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

4- 5


4.1 Using Expressions, Operators, and
Functions in Visual Basic .NET Statements
(cont.)

4- 6

• Expressions
– Single values or a combination of values,
operators, and/or functions that reduce to a single
value.
– Evaluated by calculation or manipulation.
– Result in numeric, string, or Boolean values.
McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

4.1 Using Expressions, Operators, and 4- 7
Functions in Visual Basic .NET Statements
(cont.)

• Operators
– Symbols for a common operations such as
addition or multiplication.
– Most operators are binary operators.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.


4.1 Using Expressions, Operators, and
Functions in Visual Basic .NET Statements
(cont.)
• Functions
– Descriptive names that specify a more complex
operation than that performed by an operator.
– Names are always followed by parentheses.
– The value between the parentheses is called the
argument.
– The resulting value is called the return value.
McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

4- 8


4.1 Using Expressions, Operators, and
Functions in Visual Basic .NET Statements
(cont.)
• More Complicated Expressions
– Operators and functions can be composed into
complicated expressions.
– A function’s argument may be complex.
• Ex. X = Math.Sqrt(10 + Math.Sqrt(Y + 29))

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

4- 9


4.1 Using Expressions, Operators, and 4-10
Functions in Visual Basic .NET Statements
(cont.)

• Expressions as a Part of Statements
– An expression is always a part of a statement.
• Ex. Z = Math.Sqrt(X + 2 + Y) + Math.Sqrt(4)

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.


4.2 Arithmetic Expressions

• Arithmetic operators and functions must be
written according to Visual Basic .NET syntax.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

411


4.2 Arithmetic Expressions (cont.)
• Arithmetic Operators and Operator Precedence
– Arithmetic operations must adhere to the
following order:
1. Exponentiations
2. Unary negations
3. Multiplications and Divisions
4. Integer divisions
5. Modulus operations
6. Additions and Subtractions
McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All

rights reserved.

412


4.2 Arithmetic Expressions (cont.)

• Integer Division
– Calculates the number of times one integer goes
into another, discarding the reminder.
– Mod calculates the reminder when one integer is
divided by another.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

413


4.2 Arithmetic Expressions (cont.)

• Arithmetic Functions
–
–
–
–
–
–

–

Math.Sqrt()
Math.Abs()
Math.Sign()
Fix()
Math.Exp()
Math.Log()
Rnd()

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

414


4.2 Arithmetic Expressions (cont.)
• Type Conversion Functions
– A number of functions will convert values from
one type to another.
•
•
•
•

CBool()
CDbl()
CDec()

CInt()

McGraw Hill/Irwin

CLng()
CShort()
CSng()
CStr()

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

415


4.2 Arithmetic Expressions (cont.)
• Avoiding Arithmetic Errors
– We must write arithmetic expressions carefully.
– We must avoid certain pitfalls.
– Overflow Errors
• Occur when computer attempts to store a number
that is too large for its data type.

– Roundoff Errors
• Occur when floating-point values or certain
variables are used in a program.
McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

416


4.2 Arithmetic Expressions (cont.)

– Problems Caused by Limited Significant Digits
• Limitations on the number of significant digits.
• Digits may be loss at run time.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

417


4.3 String Expressions
• Manipulate strings using string operators and
functions.
– String Operators
• & is the only string operator in Visual Basic .NET.
• Joining two string values is called concatenation.

– Functions Used with Strings
• Format()
– Converts a numeric value to a string and formats it.

• Left(), Right(), and Mid()

– Selects specific character(s) in a string.
McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

418


4.3 String Expressions

419

– Functions Used with Strings (cont.)
• StrConv()
– Converts a string into a new string using conversion
rules.

• LTrim(), Rtrim(), and Trim()
– Remove leading and trailing spaces.

• Len()
– Determines the number of characters in a string.

• Space()
– Indicates the number of spaces to create.
McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

4.3 String Expressions
– Functions Used with Strings (cont.)
• InStr()
– Conducts a string search.

• Asc() and Chr()
– Access values in the ANSI table.

• Replace()
– Perform a search and replace routine.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

420


4.4 The Try/Catch Block Revisited

• Used to detect and respond to error conditions.
• Can handle multiple error conditions.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

421


4.6 Logical Expressions

422

• Used to select an action from alternative actions.
• Results in a True or False answer to a test.
• Also known as Boolean expressions.
– Comparison Operators
•
•
•
•
•
•

<
<=
>
>=
=
<>

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

4.6 Logical Expressions (cont.)

423

– Comparison of Strings
• Strings are ranked alphabetically.

– Logical Operators
• Combine simple logical expressions to create more
complex expressions.
• Common operators are Not, And, and Or.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.


4.6 Logical Expressions (cont.)
– Logical Functions
• Common ones are IsNumeric() and IIf().
• IsNumeric() is True if the argument is a valid
number.
• IIf() chooses between two alternate paths.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All

rights reserved.

424


Chapter Summary
• Expressions are part of a statement.
• Expressions can be numeric, string, or logical.
• Expressions consist of constants, variables,
operators, and functions.
• An operator is a symbol that specifies a simple
operation.

McGraw Hill/Irwin

©2002 by The McGraw-Hill Companies, Inc. All
rights reserved.

425