Writing Software
Kashef Mughal
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Algorithms
 The term algorithm (pronounced AL-go-rith-um)
is a procedure or formula for solving a problem.
 An Algorithm describes the program in a step by
step manner
 In order to solve a business problem using a
program, we have two choices
 Procedure-Oriented approach
 Object-Oriented approach
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Solving the Problem Using a
Procedure-Oriented Approach
 Emphasis of a program is on how to
accomplish a task
 A flowchart uses standardized symbols to
show the steps needed to solve a problem
 Pseudocode uses English phrases to
describe the required steps
 User has little, if any, control
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Solving the Problem Using
an Object-Oriented/Event-Driven
(OOED) Approach
 Object-oriented/Event-driven
 Emphasis of a program is on the objects included
in the interface and the events that occur on those
objects
 You will use a TOE (Task, Object, Event) chart to
assist you in planning your object-oriented/eventdriven programs
 User has a lot of control
 Users can enter information in any order, change
what they entered at any time, and calculate a
subtotal whenever they like
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Sample TOE Chart
Task
Object
Event
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Using Variables to Store Information
 Besides storing data in the properties of
controls, a programmer also can store data,
temporarily, in memory locations inside the
computer
 The memory locations are called variables,
because the contents of the locations can
change as the program is running
 You can enter and store data in the box, but
you cannot actually see the box
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Using Variables to Store Information
 You can also store the data contained in a
control’s property in a variable
 All variables have:
 Data type – kind of data the variable can contain
 Name – An identifier the programmer creates to
refer to the variable
 Value – Every variable refers to a memory location
that contains data. This value can be specified by
the programmer. This process is called assignment
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Selecting a Data Type for a Variable
Type
Size (Bytes) Type
Size (Bytes)
Byte
1
Short
2
Char
2
Integer
4
Boolean
4
Long
8
Decimal
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Single
4
Double
8
String
Varies
Date
8
Object
Anything
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Choose the Correct Data Type
Short, Integer, Long
Used to store whole numbers
Single, Double
Store floating-point numbers
Decimal
Stores numbers with a decimal point
Boolean
Stores True and False
Char
Stores one Unicode character
Byte
Stores 8-bits of data
Date
Stores date and time information
String
Stores a sequence of characters
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Selecting a Name for a Variable
 You should assign a descriptive name to each
variable used in an application
 The name should help you remember the
variable’s data type and purpose
 Hungarian Notation is a common standard for
variable names. The figure below lists the three
characters typically associated with the Visual
Basic .NET data types using Hungarian Notation
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11
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Declaring a Variable
 To declare a VB .NET variable, write:




Keyword “Dim”
Name to be used for identifier
Keyword “As”
Data type
 Example:
' declare a variable
Dim intA As Integer
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Assigning Data to an Existing Variable
 A value can be assigned by the programmer to a
variable
 Assignment operator (=) assigns the value on the
right to the variable named on the left side
 Example:
' populate the variable
intA = 1
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In-Class Exercises
 Try the following exercises
 Pages 45,46
 Pages 49, 50
 Page 52
 Page 54
 Review the results with me
 Any questions?
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Working with Strings
 A String is a collection of characters
 We use double quotes to mark its beginning and
end (delimit)
 For example dim s as string used to declare it
 Concatenation means combining data
 Substring is a subset of any string
 Formatting of strings is a big concern especially
from a user stand point
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Concatenating Strings

Connecting strings together is called concatenating

You use the concatenation operator, which is the ampersand
(&), to concatenate strings in Visual Basic .NET

When concatenating strings, you must be sure to include a
space before and after the concatenation operator
Example
Result
“Hello “ & strFirstName
Hello Mary
strFirstName & “ sold $“ & sngSales & “.”
Mary sold $1000.
intUnits & sngSales
2001000
intUnits + sngSales
1200
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String Operations
 .Length - gets the number of characters in the
string
 .Substring - retrieves a substring from the string
 .Format - Replaces each format item in a
specified string
 .Replace - Replaces all occurrences of a specified
string with another String
 .Trim - Removes all occurrences of white space
characters from the beginning and end of the
string
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Working with Dates
 This data type has the most properties and
methods out of all the data types
 When assigning to a variable, should qualify with
# like for today it would be #1/14/2004#
 Date.Now - Gets date time that is the current local
date and time on this computer
 .DatePart - Returns an Integer value containing
the specified component of a given Date value
 Dates also have a number of methods for
formatting as these can vary from one region
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The Scope of a Variable
 A variable’s scope indicates which procedures in an
application can use the variable
 The scope is determined by where the Dim, Public or
Private statement is entered
 When you declare a variable in a procedure, the
variable is called a local variable and is said to have
procedure scope
 When you declare a variable in the form’s
Declarations section, the variable is called a formlevel variable and is said to have module scope
 Module includes all the procedures
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Creating a Local Variable
 Created with the Dim statement
 The Dim statement is entered in an object’s event
procedure e.g. Private Sub ...
 Only the procedure in which it is declared can
use the variable
 Removed from memory when the procedure ends
 Preferred way of coding
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Creating a Form-level Variable
 Created with the Private statement
 Entered in a form’s General declarations section
 Can be used by any of the procedures in the form
 Removed from memory when the form is
destroyed
 Should be used on a limited basis
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Creating a Global Variable
 Created with the Public statement
 Best place for this is in a new module like
basMain
 This can be used by any procedure in any module
 Removed from memory when the application
ends
 Should also be used on a limited basis. An
example would be connection to a database
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Constants
 It refers to a memory location whose contents
cannot be changed while the program is running
 Constants are usually declared globally
 Examples:
 conPi
 conRate
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Creating a Constant
 A memory location whose value cannot change
during run time
 Syntax: [Public|Private] Const constname [As
datatype] = expression
 Examples:
 Const conPi As Single = 3.141593
 Public Const conMaxAge as Integer = 65
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In-Class Exercises
 Try the following exercises
 Pages 56 through 75 labeled “Try It Out”
 Review any problems with me
 Any questions?
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Number Systems
 Humans use Base-10 number system
 Computers prefer Base-2 number system
 Review the differences on Page 77
 A memory slot in a computer is called a bit
 8 bits make up a byte
 Everything is in terms of power of 2 , so 1 KB is
really 210 which is equal to 1024 bytes
 Review the conversions shown in the book
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Methods
 A method is a block of code that does something
 Helps to break up a program into pieces
 Lets you re-use the code
 We pass data (parameters) to a method which in
turn returns (results) back to us
 Two types of methods
 Sub (sub procedure or sub routine)
 Function
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Sub vs. Function
 A function is used when we need a block of code
to do something and then return a value back. For
example a function to calculate area
 A sub is used when we do not need a return
value. For example if user clicks on a button do
something.
 We have been working with a sub already
 Private Sub .. End Sub
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Debugging an Application
 Errors are common in computer applications
 Two kinds of Errors
 Compile Error
 Run-time Error
 More in Chapter 11
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In-Class Exercises
 Try the following exercises
 Pages 85
 Pages 87
 Page 89
 Page 91
 Page 93
 Review Questions on Page 95
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