Introduction to Programming Fundamentals of Programming in Visual Basic

Outline and Objective Visual Basic Objects Visual Basic Events Numbers Strings Input/Output Built-In Functions

The Initial Visual Basic screen Toolbox Project Explorer window Properties window Form Toolbar Menu bar

Steps to Create a Visual Basic Program 1. Create the Objects 2. Set Properties 3. Write the Code for each Event

Four most useful Visual Basic Controls Text Boxes Labels Command Buttons Picture Boxes

A Text Box Walkthrough: Double-click on Text Box to add a Text Box to your form Activate the Properties window (Press F4) Set values of Properties for Text Box

A Text Box Walkthrough Text box

Some Useful Properties: Name Caption Border style Visible Back Color Alignment Font

Naming Objects: Use the Property window to change the Name property of an object Good Programming habit is that each name begins with three letter prefix that identifies the type of control.

Naming Objects:

Visual Basic Events Code is a set of statements that will be executed when you run a program. Write Code for each Event. Most Events are associated with Objects. The code for each event is called an “Event Procedure”.

The steps for creating a VB program: Create the Interface. Set Properties for the objects. Write the code that executes when event occurs.

An Event Procedure Walkthrough Create the interface. Set Properties. Double click on the object to open the Code window. Click on the Procedure box to find the event Write the code for that event.

Example of An Event Private Sub objectName_event ( ) statements End Sub Private Sub txtOne_GotFocus( ) txtOne.Font.Size = 12 txtOne.Font.Bold = False End Sub

More Example Private Sub cmdButton_Click( ) txtBox.ForeColor = vbRed txtBox.Font.Size = 24 txtBox.Text = “Hello” End Sub

Components of Visual BASIC Statements Variables Keywords (reserved words) Constants

Variables A storage location in main memory whose value can change during program execution. These storage locations can be referred to by their names. Every variable has three properties: a Name, a Value, and a Data Type. Types of variables: Numeric and String

Rules for Creating Variable Names Must begin with a letter. Can contain letters, numeric digits. Can have up to 255 characters. Can Not be restricted keyword.

Numeric Variables Used to store Numbers. The value is assigned either by the programmer or by calculation.

Valid Numeric Variable Names: timeElapsed taxRate speed n celsius

Invalid Numeric Variable Names: maximum/average 1stChoice square yard

Constant Similar to a variable, but can NOT change during the execution of a program. Types of Constants: numeric constants string constants

Valid Numeric Constants: Integer Real number

Invalid Numeric Constants: 14, % 33- $ &

Numeric Constants in a Statement: tax = 0.02 * (income * dependence) sum = 2 + x y

String Constants: A group of alphanumeric data consisting of any type of symbols.

Valid String Constants “A rose by any other name” “Down By the Sea Shore” “134.23” “She said, ‘stop, thief!’”

Invalid String Constants ‘Down by the Seashore’ “ “She said, “Stop, thief!””

Arithmetic Operations & Hierarchy of Operations Operator Operation Basic expression ^ Exponentiation A ^ B * Multiplication A * B / Division A / B + Addition A + B - Subtraction A - B

Examples Evaluate the following expressions: x = 3 * / 3 x = 4 ^ (8 / 4) y = / (3 * (10 - 9)) z = ^ 2 m = 6 / 3 + 3

Keywords Words that have predefined meaning to Visual Basic. Can Not be used as variable names. Example: Print Cls If While

Visual Basic Print Statement Print: Is a method used to display data on the screen or printer. Can be used to print value of variables. Can be used to print value of arithmetic expressions.

Example of Print Statements Private Sub cmdCompute_Click() picResults.Print picResults.Print 3 * 2 picResults.Print 3 / 2 picResults.Print 3 ^ 2 picResults.Print 2 * (3 + 4) End Sub

Example of Print Statement picOutput.Print speed picOutput.Print taxRate picOutput.Print “Class average is”; total / 3

Example x = 15 y = 5 picOutput.Print (x + y) / 2, x / y

Output 10 3

Internal Documentation An apostrophe (‘) can be used to indicate comments; comments are ignored by Visual Basic. The keyword Rem can also be used instead of an apostrophe for comments. Remarks can also be placed after program statement too.

Visual Basic Assignment Statement The statement var = expr assigns the value of the expression to the variable. Assigns the value of the expression on the right to the variable on the left.

Example Private Sub cmdCompute_Click( ) picResults.Cls a = 5 b = 4 c = a * (2 + b) picResults.Print c End Sub

Valid Assignment Statement count = count + 1 num = 5 count = count + num /2

Invalid Assignments 10 = count count + 1 = count

String Variables A String variable stores character strings. The rules for naming string variables are identical to those of numeric variables. When a String variable is first declared, its value is the null string. (that is, the empty string).

Example of String Variable Private Sub cmdShow_Click() picOutput.Cls phrase = "win or lose that counts." picOutput.Print "It's not whether you "; phrase picOutput.Print "It's whether I "; phrase End Sub

Concatenation Two string can be combined with the concatenation operation. Concatenation is represented with the ampersand ( & ) sign.

Example of Concatenation: strVar1 = “Hello” strVar2 = “World” picOutput.Print strVar1& strVar2

Example of Concatenation txtBox.Text = “32” & CHR(176) & “ Fahrenheit”

Data Types Each variable in the program is assigned to a data type.

Declaring Variable Types Use the Dim statement to Declare the type of a variable. Example: Dim number As Integer Dim flower As String Dim interestRate As Single

Data Types : Single-precision numeric variable: Stores real numbers Double-precision numeric variable: Stores real numbers with many digits Integer: Stores integers Long integer: Stores integers with many digits

Using Text Boxes for Input/Output The contents of a text box are always a string. Numbers are also stored in text boxes as strings.

Using Text Boxes for Input/Output Therefore, the contents of a text box should be changed to a number before being assigned to a numeric variable. Val (txtBox.Text) changes the input string into a number. Example: numVar = Val (txtBox.Text)

Example (convert miles to furlong and vice versa) Private Sub txtFurlong_LostFocus() txtMile.Text = Str(Val(txtFurlong.Text / 8)) End Sub Private Sub txtMile_LostFocus() txtFurlong.Text = Str(8 * Val(txtMile.Text)) End Sub

The KeyPress Event Procedure Private Sub txtCharacter_KeyPress(KeyAscii As Integer) txtCharacter.Text = "" picOutput.Cls picOutput.Print Chr(KeyAscii); " has ANSI value"; KeyAscii End Sub

Reading Data from Files 1. Choose a number to be the reference number to the file. 2. Set the mode in which the file is to be used: Input Output Append 3. Read the data sequentially using Input statement. 4. Close the file.

Example of Reading from a File: Open “DATA.TXT” for Input As #1 Input #1, num1 Input #1, num2 picOutput.Print num1+num2 Close #1 Reference number Read the data and assign it to num1 Open the file Read from the file Close the file

Example of Reading from a File: Open “Data.txt” for Input As #1 Input #1,num1, num2 picOutput.Print num1+num2 Close #1

Input from an Input Box: Use Text Box to obtain input. For one piece of input use input box instead of a text box Input Box is a predefined dialog box.

Syntax for an Input Box stringVar = InputBox (prompt, title)

Example of Input Box Private Sub cmdDisplay_Click() Dim fileName As String, prompt As String, title As String Dim houseNumber As Single, street As String prompt = "Enter the name of the file containing the information." title = "Name of File" fileName = InputBox(prompt, title) Open fileName For Input As #1 Input #1, houseNumber Input #1, street picAddress.Print "The White House is at"; houseNumber; street Close #1 End Sub After executing an input box would pop up

Using Message Box for Output: Use message box to get the user’s attention. Message box is a predefined dialog box too.

Syntax for Message Box MsgBox prompt,, title

Example of Message Box MsgBox “Nice try, but no cigar”,, “Consolation” Stays on the screen until the user presses OK

Formatting the Output: Create user friendly output. In the Print method, control of the spacing of the output is controlled by the following devices.

Formatting the Output: Semicolon Comma Tab Function

Semicolons The next value output is placed in the next column position. Example: picOutput.Print “Patrick”; ”Jon” Output Screen: PatrickJon

Example of Semicolon picOutput.Print “Patrick”; ” Jon” Output Screen: Patrick Jon Space here

Example of Semicolon picOutput.Print 100; -200; 300 Output Screen: One space Two spaces

Commas The next value output is placed in the next available print zone.

Print Zones Each print zone is 14 positions wide.

Example of Print Zone Example: picOutput.Print “SEE”, ”YOU”, ”SOON” Output Screen: SEE YOU SOON Column 1 Column 15 Column 29

Example of Commas A print zone can be skipped by typing consecutive commas Example: picOutput.Print “HOURLY”,, “PAY” Output Screen: HOURLY PAY Column 29

Tab Function Starts output in the specified column. It provides more flexibility in formatting. Only use Semicolons with the Tab function. Only can be used to advance the print position.

Example of Tab Function Example: picOutput.Print Tab(3); “Hi there!” ;TAB(25) ;“Bye!” Output Screen: Hi there! Bye! Column 3 Column 25

Example of Tab Example: picOutput.Print TAB(25); 5; TAB(15); 4; TAB(5); 3 Output Screen: Column 25 Column 15 Column 5

Functions: What is a function? What are advantages of using functions? How do you use a function?

What is a function A sub program designed to perform a specific task. A sub program designed to return a single value to the calling program.

Types of Functions Built-In functions (library) User-defined functions

Example x = Sqr(225) y = Int (2.7) str1 = Left (“John Smith”, 4) number = Rnd

Types of Standard Functions Numeric Functions (manipulate numbers) String Functions (manipulate strings)

Numeric Functions

Example of Numeric Functions Private Sub cmdEvaluate_Click() Dim n As Single, root As Single picResults.Cls n = 6.76 root = Sqr(n) picResults.Print root; Int(n); Round(n,1) End Sub

Commonly-Used String Functions Function: Left (“Penguin”,4) Purpose: Returns the number of specified characters, starting at the beginning of the string.

Commonly-Used String Functions Function: Right (“Gotham City”, 4) Purpose: Returns the number of specified characters from the end of the string.

Commonly-Used String Functions Function: Mid (“Commissioner”, 4, 3) Purpose: Returns the character string starting at the position indicated by the first number and continuing for the length specified by the second number.

Commonly-Used String Functions Function: UCase (“Yes”) Purpose: Converts any lowercase letters in string to uppercase.

String-Related Numeric Functions Function: InStr (“John Smith”, ” “) Purpose: Searches for the first occurrence of one string in another and gives the position at which the string is found.

String-Related Numeric Function Function: Len (“John Smith”) Purpose: Returns the number of characters in the string.

Format Function The format functions provide detailed control of how numbers, dates, and strings are displayed.

Examples of Format Functions FormatNumber ( , 1) 12,345.6 FormatCurrency ( , 2) $12, FormatPercent (.185, 2) 18.50% FormatNumber (1 + Sqr(2), 3) 2.414

Format Function Format (expr, Purpose: The value of this function contains the string right justified in a field of n spaces. Where n is a string of symbols.

Examples: Format (12345, Format (123, 123 Format (“123.4”, 123.4

Example FormatDateTime (“ ”, vbLongDate) Output: Wednesday, September 15, 1999

Rnd Function Returns a random number from 0 up to 1. (excluding 1). Example: Displays a random integer from 1 through 6. picBox.Print Int(6 * Rnd) + 1

Examples of Using Rnd Function: An integer from 1 through 100? A number from 2 through 4 (excluding 4)? An even integer from 2 through 100 ? Either 0 or 1?