Matakuliah
Tahun
: T0063 – Pemrograman Visual
: 2009
Performing Calculations and Manipulating
Data: Expressions
CHAPTER FOUR
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
Expressions
Operators
Functions
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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()
CLng()
• CDbl()
CShort()
• CDec()
CSng()
• CInt()
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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4.5 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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