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

Chapter 4 Performing calculations and manipulating data Expressions. The following will be discussed in this chapter 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.

CHAPTER FOUR

Performing Calculations and Manipulating Data: Expressions

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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

4.1 Using Expressions, Operators, and

Functions in Visual Basic NET Statements

• An expression tells the computer to manipulate

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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.

4.1 Using Expressions, Operators, and

Functions in Visual Basic NET Statements

(cont.)

• 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.

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4.1 Using Expressions, Operators, and

Functions in Visual Basic NET Statements

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.

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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))

4.1 Using Expressions, Operators, and

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)

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4.2 Arithmetic Expressions

• Arithmetic operators and functions must be

written according to Visual Basic NET syntax

4.2 Arithmetic Expressions (cont.)

• Arithmetic Operators and Operator Precedence

– Arithmetic operations must adhere to the

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4.2 Arithmetic Expressions (cont.)

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4.2 Arithmetic Expressions (cont.)

• Type Conversion Functions

– A number of functions will convert values from

one type to another.

4.2 Arithmetic Expressions (cont.)

• Avoiding Arithmetic Errors

– We must write arithmetic expressions carefully.

– We must avoid certain pitfalls.

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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.

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()

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• LTrim(), Rtrim(), and Trim()

– Remove leading and trailing spaces.

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4.4 The Try/Catch Block Revisited

• Used to detect and respond to error conditions

• Can handle multiple error conditions

4.6 Logical Expressions

• Used to select an action from alternative actions

• Results in a True or False answer to a test

• Also known as Boolean expressions

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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.

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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

Chapter Summary (cont.)

• A function is a name that represents a complex

operation

• Function names always end in parentheses

• Arithmetic expressions consists of numeric

constants, variables, arithmetic operators, and

functions

• Arithmetic expressions are evaluated using

order of precedence rules

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Chapter Summary (cont.)

• Errors may occur when evaluating expressions

• String expressions consist of string constants

and variables and string operators and functions

• Chr() and Asc() are used with strings to access

the ANSI table

• Logical expressions are composed of variables, constants, comparison operators, logical

operators, and logical functions

Chapter Summary (cont.)

• A logical expression has the form of a

True/False question

• Comparison of numeric values is

straightforward

• Comparison of string values is more complex

• The logical function IIf() is used to choose one of two expressions