CHAPTER FOUR
Performing Calculations and
Manipulating Data: Expressions
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Expressions
• Arithmetic expressions
– To perform arithmetic operations.
• String expressions
– To manipulate string data.
• Logical expressions
– To select an appropriate action.
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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.
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4.1 Using Expressions, Operators, and
Functions in Visual Basic .NET Statements
• 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.
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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.
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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
(cont.)
• Operators
– Symbols for a common operations such as
addition or multiplication.
– Most operators are binary operators.
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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))
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4.1 Using Expressions, Operators, and
Functions in Visual Basic .NET Statements
(cont.)
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• 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.
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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
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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.
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4.2 Arithmetic Expressions (cont.)
• Arithmetic Functions
–
–
–
–
–
–
–
Math.Sqrt()
Math.Abs()
Math.Sign()
Fix()
Math.Exp()
Math.Log()
Rnd()
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4.2 Arithmetic Expressions (cont.)
• Type Conversion Functions
– A number of functions will convert values from
one type to another.
•
•
•
•
CBool()
CDbl()
CDec()
CInt()
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CLng()
CShort()
CSng()
CStr()
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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.
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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.
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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.
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4.3 String Expressions
– 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.
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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.
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4.4 The Try/Catch Block Revisited
• Used to detect and respond to error conditions.
• Can handle multiple error conditions.
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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.
– Comparison Operators
•
•
•
•
•
•
<
<=
>
>=
=
<>
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4.6 Logical Expressions (cont.)
– 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.
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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.
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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.
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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.
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