Variables Continued In the last session we saw how variables are objects that allow us to store values in the RAM of the computer In this session we shall take a look at: Some other variable data types Different tasks you may perform with different data types

Additional Data Types The following code is taken from the Widget Swap program (btnSave of aswap.aspx). Notice some new data types.

The Date Data Type What if I asked you to add 200 days to today’s date? In VB.NET using the date data type it is easy... Dim MyDate As Date Dim NewDate As Date MyDate = "23/4/2010" NewDate = MyDate.AddDays(200)

The Decimal, Integer & Byte Data Types All numeric data types. They differ in the kinds of number they store Byte and Integer may only store whole numbers Byte cannot store negative numbers and is limited to a range of 0 to 255 Integer has a range from -2,147,483,648 to 2,147,483,647 but like byte cannot store decimals If we want to store larger numbers than those above or want to store decimal values e.g. currency we need to use the decimal data type. The decimal data type has a range of +/- 79,228,162,514,264,337,593,543,950,335

Rounding Decimal Numbers Since the decimal data type tends to go a bit over the top with the number of decimal places it is worth knowing how to round decimal numbers. The Math.Round method will do this. Dim Price As Decimal Price = txtPrice.Text = Math.Round(Price, 2) The above code would round the price to 2 decimal places.

Mathematical Processing Addition. Addition operator.+ Dim MyVariable As Integer MyVariable = Subtraction. Subtraction operator- Dim MyVariable As Integer MyVariable = 5 – 2 Multiplication. The multiplication operator* Dim MyVariable As Integer MyVariable = 15 * 2 Division. The division operator / Dim MyVariable As Integer MyVariable = 30 / 2

The String Data Type & Concatenation Concatenation involves the joining together of smaller strings to form larger strings.

The Boolean Data Type The Boolean data type is used to store the results of Boolean logic that is based only on the values True and False. Boolean variables may only store either True or False. Later in the module we shall use the validation function called IsNumeric which we will use to check if something is a number or not. The following code gives you some idea of how it works... Dim OK As Boolean OK = IsNumeric("Fred")

Why don’t we just use Controls and Abandon Variables? Take a look at the following code… Why don’t we just rewrite the code as follows?

Two Reasons Controls have a visual component they are more demanding on system resources. A variable is a much more “light weight” object. Any code that constantly uses controls to perform processing will run slower than the same code written using variables. Controls are typeless and run the risk of producing strange results.

Unexpected Results Imagine we have the following program that adds two numbers together. What do you expect will happen when we press Add? The click event for “Add” contains the following code...

The Result… The problem is that instead of performing a numeric operation the code performs a string operation. It concatenates rather than adds. This is one example of the unpredictable results that may happen if we use controls and not variables.

Questions 1. What is wrong with the following variable declarations? Dim My Name As String Dim MyName As Integer Dim Age As Decimal Dim Price As Byte Dim Password As Boolean Dim OK As Integer

Questons 2. Plan out a program that takes two numbers, multiplies them and displays the result. What inputs are required? What outputs are required? Declare the variables for the inputs and outputs Assign values to the input variables Write the code that calculates the answer Display the result on the web form