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Ppt lesson 05

Ppt lesson 05






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    Ppt lesson 05 Ppt lesson 05 Presentation Transcript

    • Microsoft Visual Basic 2005 BASICS Lesson 5 Data Types and Variables
    • Objectives
      • Describe the purpose of data types and variables.
      • Use the AutoSize property.
      • Declare and use variables.
      • Describe the scope of variables.
      • Describe the Object data type.
    • Data Types
      • Computers are all about data.
      • Visual Basic supports a certain set of data types.
      • You can choose to store data in memory locations called variables.
      • Variables
        • Can be used to store and manipulate all kinds of data
    • Data Types (cont.)
    • Using the AutoSize Property
      • The AutoSize property
        • Adjusts the size of a control to fit its contents
      • Label control example
        • The AutoSize property will shrink or enlarge the label to fit the text.
    • Using the AutoSize Property (cont.)
    • Using the AutoSize Property (cont.)
    • Declaring Variables
      • Using a variable in your programs
        • Let the compiler know
          • That you want to set up a memory location as a variable
          • What you want to call the variable
          • What data type you want the variable to have
      • Declare a variable
        • Use the Dim statement
    • Rules for Naming Variables
      • When naming variables, keep the following rules in mind:
        • Variable names must begin with an alphabetic character.
        • Following the first character, letters, numbers, and underscores are allowed.
        • Variable names cannot include spaces.
        • Variable names can be 255 characters long.
    • Rules for Naming Variables (cont.)
    • Using Variables
      • Variables can be used in the same way as labels and text boxes.
      • Use the assignment operator to assign a value to a variable.
        • You can also assign hard-coded values to a variable.
    • Using Variables (cont.)
      • Use mathematical operators to perform calculations with numeric variables.
      • Output the value in a variable.
        • Assign the value to a label.
    • Using Variables (cont.)
    • Using Variables (cont.)
    • Scope
      • The term “scope” refers to the reach of a variable.
      • General rule
        • You should declare variables as locally as possible.
    • Three Levels of Scope
      • Levels
        • Local variable
          • Declared within an event procedure
        • Form-level variable
          • Declared in the Declarations section of a form’s Code window
        • Global variable
          • Declared in a code module’s section
    • The Declarations Section
      • Access the Declarations section
        • Select (Declarations) from the Method Name list that appears at the top of the Code window.
    • The Declarations Section (cont.)
    • The Declarations Section (cont.)
    • Using the Object Data Type
      • Object data type
        • Very flexible
        • Can store many different types of variables
      • Object variables
        • Can be declared by specifying the Object type
        • Or by declaring a variable without a type
    • Summary
      • Data can be in the form of numbers, text, dates, pictures, and even sound.
      • Visual Basic supports a set of data types. There are data types for whole numbers, floating-point numbers (decimals), text, dates, and more.
      • You can choose to store data in memory locations called variables.
    • Summary (cont.)
      • The AutoSize property will adjust the size of a control to fit its contents.
      • The first step to using a variable is to declare it using the Dim statement.
      • When naming variables, keep the naming rules in mind. It is a good idea to use naming prefixes to identify the data type of the variable.
    • Summary (cont.)
      • You can assign values to variables using the assignment operator.
        • You can also use the other mathematical operators with numeric variables.
      • A variable’s scope indicates the procedures that have access to the variable. A variable’s scope can be local, form-level, or global.
    • Summary (cont.)
      • The Declarations section of a form’s Code window allows you to declare form-level variables.
      • The Object data type can hold many different kinds of data, but is less efficient than specific data types.