Variables and Arithmetic Operations CHAPTER FOUR Variables and Arithmetic Operations

Objectives Create, modify, and program a TextBox object Use code to place data in the Text property of a Label object Use the AcceptButton and CancelButton properties Understand and declare String and Numeric variables Use assignment statements to place data in variables Chapter 4: Variables and Arithmetic Operations

Objectives Use literals and constants in coding statements Understand scope rules for variables Convert string and numeric data Understand and use arithmetic operators and arithmetic operations Chapter 4: Variables and Arithmetic Operations

Objectives Format and display numeric data as a string Create a form load event Create a concatenated string Debug a program Chapter 4: Variables and Arithmetic Operations

Introduction Chapter 4: Variables and Arithmetic Operations

TextBox Objects With Visual Studio open, the Desktop application created, and the [Design] tabbed page visible, point to the TextBox .NET component in the Toolbox Drag the TextBox .NET component onto the Windows Form object at the desired location When the upper-left corner of the pointer is located where you want the TextBox object’s upper-left corner, release the left mouse button Chapter 4: Variables and Arithmetic Operations

TextBox Objects Chapter 4: Variables and Arithmetic Operations

Sizing and Positioning a TextBox Object Select the TextBox object. Select the (Name) property and type the desired name. Scroll in the Properties window until the Text property is visible and then tap or click the right column for the Text property Type the maximum number of characters the user normally will enter into the text box and then press the ENTER key. Programmers often use the digit 8 in this situation because it is wider than other digits Chapter 4: Variables and Arithmetic Operations

Sizing and Positioning a TextBox Object Using the Properties window, change the Font property to the correct font and font size. Then, drag the right edge of the TextBox object and resize it to be slightly wider than the entry To horizontally align the text in the label and the text in the text box, drag the text box up until a red snap line indicates the bottoms of the text are aligned. Then, release the left mouse button Chapter 4: Variables and Arithmetic Operations

Sizing and Positioning a TextBox Object Chapter 4: Variables and Arithmetic Operations

Aligning Text in a TextBox Object Select the TextBox object. In the Properties window, scroll until the TextAlign property is visible, tap or click the TextAlign property in the left column, and then tap or click the list arrow in the right column of the TextAlign property Tap or click the desired alignment option in the TextAlign property list Because the TextBox object is sized properly, remove the digits in the TextBox object. Select the characters in the Text property, press the DELETE key on your keyboard, and then press the ENTER key Chapter 4: Variables and Arithmetic Operations

Aligning Text in a TextBox Object Chapter 4: Variables and Arithmetic Operations

Creating a MultiLine Text Box Select the TextBox object, tap or click the Action tag, and then point to the MultiLine check box Tap or click the MultiLine check box Chapter 4: Variables and Arithmetic Operations

Creating a MaskedTextBox Object Chapter 4: Variables and Arithmetic Operations

Creating a MaskedTextBox Object Drag a MaskedTextBox .NET component from the Toolbox to the Windows Form object. Then, tap or click the Action tag on the TextBox object and point to the Set Mask command Tap or click Set Mask on the MaskedTextBox Tasks list and then tap or click the desired mask description in the Input Mask dialog box Tap or click the OK button in the Input Mask dialog box and then tap or click anywhere in the Windows Form object Chapter 4: Variables and Arithmetic Operations

Creating a MaskedTextBox Object Chapter 4: Variables and Arithmetic Operations

Label Objects Drag a Label object onto the Windows Form object to the correct location. Enter the desired name for the label. Change the label to the appropriate font size. In the Text property for the Label object, enter the maximum number of characters that will appear in the label during execution of the program Drag the Label object up until the red snap line appears. Then release the Label object Chapter 4: Variables and Arithmetic Operations

Label Objects Chapter 4: Variables and Arithmetic Operations

Accept Button in Form Properties After the Button objects are added, tap or click a blank area in the Windows Form object to select it. Scroll in the Properties window until the AcceptButton property is visible. Tap or click the AcceptButton property name in the left column and then tap or click the AcceptButton property list arrow in the right column Tap or click the desired button in the AcceptButton property list Chapter 4: Variables and Arithmetic Operations

Accept Button in Form Properties Chapter 4: Variables and Arithmetic Operations

Cancel Button in Form Properties When the user presses the esc key, the event handler processing will be executed for the button identified as the Cancel button Tap or click a blank area in the Windows Form object to select it Tap or click the CancelButton property name in the left column in the Properties window for the Windows Form object, and then tap or click the CancelButton list arrow Tap or click the desired button name in the CancelButton property list Chapter 4: Variables and Arithmetic Operations

Visual Studio Preparation for Code Entry With the Toolbox visible, tap or click the Toolbox Close button. The Toolbox closes and the work area expands in size. To display the Toolbox after it has been closed, tap or click the View menu and then tap or click Toolbox Chapter 4: Variables and Arithmetic Operations

String Data Type A String data type can store any character available on the computer The data type for the value the user enters in a TextBox object and that is stored in the Text property of the TextBox object is string A variable is a named location in RAM where data is stored A String variable is a named location in RAM that can store a string value Chapter 4: Variables and Arithmetic Operations

String Data Type Chapter 4: Variables and Arithmetic Operations

Assignment Statements One method used to place data in the variable is an assignment statement Chapter 4: Variables and Arithmetic Operations

Assignment Statements With Visual Studio open to the code window and the insertion point located in the desired column, type Dim followed by a space. Then, type the name of the String variable you want to define Press the SPACEBAR, type the word As, and then press the SPACEBAR again Because the entry should be String, type str Press the ENTER key Chapter 4: Variables and Arithmetic Operations

Assignment Statements To begin the assignment statement, type the first few letters of the variable name until IntelliSense identifies the correct variable to use Press the SPACEBAR, press the EQUAL SIGN key, and then press the SPACEBAR Type the name of the text box containing the value you wish to use Press the PERIOD key and then, if necessary, type te to highlight the Text entry in the IntelliSense list Press the ENTER key Chapter 4: Variables and Arithmetic Operations

Assignment Statements Chapter 4: Variables and Arithmetic Operations

Numeric Data Types A numeric data type must be used in arithmetic operations Chapter 4: Variables and Arithmetic Operations

Numeric Data Types Chapter 4: Variables and Arithmetic Operations

Other Data Types Chapter 4: Variables and Arithmetic Operations

Other Data Types Chapter 4: Variables and Arithmetic Operations

Miscellaneous Data Types Chapter 4: Variables and Arithmetic Operations

Variable Prefixes Chapter 4: Variables and Arithmetic Operations

Literals A value is called a literal when it literally is the value required by the assignment statement Chapter 4: Variables and Arithmetic Operations

Forced Literal Types Sometimes you might want a literal to be a different data type than the Visual Basic default type Chapter 4: Variables and Arithmetic Operations

Constants A constant contains one permanent value throughout the execution of the program Chapter 4: Variables and Arithmetic Operations

Constants The declaration of a constant begins with the letters Const, not the letters Dim You must assign the value to be contained in the constant on the same line as its definition You cannot attempt to change the value of the constant anywhere in the program. If you do, you will produce a compiler error The letter c often is placed before the constant name to identify it throughout the program as a variable that cannot be changed Other than the letter c, constant names are formed using the same rules and techniques as other variable names Chapter 4: Variables and Arithmetic Operations

Referencing a Variable When a variable is declared, it will be underlined with a green squiggly line until it is referenced in a statement When using a variable in a program, it is mandatory that you define the variable before using the variable name in a statement Chapter 4: Variables and Arithmetic Operations

Scope of Variables The scope of a variable specifies where the variable can be referenced in a Visual Basic statement within the program You declare a variable in the region within a program The code between the Sub statement and the End Sub statement is a procedure A variable that can only be referenced within the region of the program where it is defined is called a local variable Local variables have a certain lifetime in the program Global variables can be used in multiple regions of a Visual Basic program Chapter 4: Variables and Arithmetic Operations

Converting Variable Data Visual Basic includes several procedures that allow you to convert one data type to another data type A procedure to convert a String data type to an Integer data type is named ToInt32 The procedure is in the Convert class, which is available in a Visual Studio 2015 class library Chapter 4: Variables and Arithmetic Operations

Using a Procedure A procedure that performs its task but does not return a value is called a Sub procedure A procedure that returns a value is called a Function procedure, or a function An argument identifies a value required by a procedure Every procedure is part of a class Chapter 4: Variables and Arithmetic Operations

Using a Procedure Chapter 4: Variables and Arithmetic Operations

Option Strict On By default, Visual Basic will automatically convert data types if the one on the right side of the equal sign in an assignment statement is different from the data type on the left side of the equal sign To prevent automatic conversion of values, the developer must insert the Option Strict On statement in the program prior to any event handler code The Option Strict On statement explicitly prevents any default data type conversions that would cause data loss and prevents any conversion between numeric types and strings Chapter 4: Variables and Arithmetic Operations

Option Strict On Chapter 4: Variables and Arithmetic Operations

Arithmetic Operations Chapter 4: Variables and Arithmetic Operations

Arithmetic Operators Chapter 4: Variables and Arithmetic Operations

Multiple Operations A single assignment statement can contain multiple arithmetic operations Hierarchy of Operations Exponentiation (^) is performed first Multiplication (*) and division (/) are performed next Integer division (\) is next MOD then occurs Addition (+) and subtraction (-) are performed last Within these five steps, calculations are performed left to right Chapter 4: Variables and Arithmetic Operations

Displaying Numeric Output Data Chapter 4: Variables and Arithmetic Operations

Format Specifications for the ToString Function Use the format specifier to identify the format for the numeric data to be returned by the ToString function Chapter 4: Variables and Arithmetic Operations

Precision Specifier The precision specifier is a number included within the quotation marks in the function call that identifies the number of positions that should be returned to the right of the decimal point Chapter 4: Variables and Arithmetic Operations

Clear Procedure The Clear procedure clears any data in the Text property of a TextBox object Chapter 4: Variables and Arithmetic Operations

Clearing the Text Property of a Label The Clear procedure cannot be used with a Label object You must write an assignment statement that assigns a null length string to the Text property Chapter 4: Variables and Arithmetic Operations

Setting the Focus When the focus is on a TextBox object, the insertion point is located in the text box Chapter 4: Variables and Arithmetic Operations

Form Load Event A form load event occurs when the program starts and Windows Form Object is loaded into computer memory Chapter 4: Variables and Arithmetic Operations

Concatenation The process of joining two different values into a single string is called concatenation The values being concatenated must be String data types Chapter 4: Variables and Arithmetic Operations

Concatenation Chapter 4: Variables and Arithmetic Operations

Class Scope When a variable is referenced in two different event handling procedures, it must be defined at the class level instead of the procedure (event handler) level Chapter 4: Variables and Arithmetic Operations

Debugging Your Program A Format Exception occurs when the user enters data that a statement within the program cannot process properly Chapter 4: Variables and Arithmetic Operations

Debugging Your Program An Overflow Exception occurs when the user enters a value greater than the maximum value the statement can process It is not possible to divide by zero, so if your program contains a division operation and the divisor is zero, the Divide By Zero Exception will occur Chapter 4: Variables and Arithmetic Operations

Program Design Chapter 4: Variables and Arithmetic Operations

Program Design Chapter 4: Variables and Arithmetic Operations

Event Planning Document Chapter 4: Variables and Arithmetic Operations

Summary Create, modify, and program a TextBox object Use code to place data in the Text property of a Label object Use the AcceptButton and CancelButton properties Understand and declare String and Numeric variables Use assignment statements to place data in variables Chapter 4: Variables and Arithmetic Operations

Summary Use literals and constants in coding statements Understand scope rules for variables Convert string and numeric data Understand and use arithmetic operators and arithmetic operations Chapter 4: Variables and Arithmetic Operations

Summary Format and display numeric data as a string Create a form load event Create a concatenated string Debug a program Chapter 4: Variables and Arithmetic Operations

Variables and Arithmetic Operations CHAPTER FOUR COMPLETE Variables and Arithmetic Operations