Teach yourself the visual basic .net Language

Teach yourself the visual basic .net Language

A Brief History of BASIC

·    The BASIC language was developed in the early 1960's at Dartmouth College as a device for teaching programming to “ordinary” people.  There is a reason it’s called BASIC:

B (eginner's)

A (All-Purpose)

S (Symbolic)

I (Instruction)

C (Code)

     

·         When timesharing systems were introduced in the 1960’s, BASIC was the language of choice.  Many of the first computer simulation games (Star Trek, for example) were written in timeshare BASIC.

·         In the mid-1970's, two college students decided that the new Altair microcomputer needed a BASIC language interpreter.  They sold their product on cassette tape for a cost of $350.  You may have heard of these entrepreneurs:  Bill Gates and Paul Allen!

·         Every BASIC written since then has been based on that early version.  Examples include:  GW-Basic, QBasic, QuickBasic.  All the toy computers of the early 80’s (anyone remember TI99/4A, Commodore 64, Timex, Atari 400?) used BASIC for programming.

     

·    Visual Basic (allowing development of Windows applications) was first introduced in 1991.  The latest (and last) version of Visual Basic is Version 6.0, which was released in 1997.

·         Visual Basic .NET still uses the BASIC language to write code.  Visual Basic .NET provides a long overdue enhancement to the language with many new features.  In addition, many archaic features than have been around since Bill and Paul’s earliest efforts have finally been retired.  This chapter provides an overview of the BASIC language used in the Visual Basic .NET environment.  If you’ve ever used another programming language (or some version of BASIC), you will see equivalent structures in the language of Visual Basic .NET.

Visual Basic .NET Statements and Expressions

·    The simplest (and most common) statement in Visual Basic .NET is the assignment statement.  It consists of a variable name, followed by the assignment operator (=), followed by some sort of expression.  The expression on the right hand side is evaluated, then the variable (or property) on the left hand side of the assignment operator is replaced by that value of the expression.

     

Examples:

StartTime = Now

lblExplorer.Text = "Captain Spaulding"

BitCount = ByteCount * 8

Energy = Mass * LIGHTSPEED ^ 2

NetWorth = Assets - Liabilities

The assignment statement stores information.

·         Statements normally take up a single line with no terminator.  Statements can be stacked by using a colon (:) to separate them.  Example:

StartTime = Now : EndTime = StartTime + 10

The above code is the same as if the second statement followed the first statement.  Be careful stacking statements, especially with If/End If structures (we’ll learn about these soon).  You may not get the response you desire.  The only place we tend to use stacking is for quick initialization of like variables.

     

·         If a statement is very long, it may be continued to the next line using the continuation character, an underscore (_).  Example:

Months = Math.Log(Final * IntRate / Deposit + 1) _

/ Math.Log(1 + IntRate)

We don’t use continuation statements very much in these notes or in our examples.  Be aware that long lines of code in the notes many times wrap around to the next line (due to page margins).

·         Comment statements begin with the keyword Rem or a single quote (').  For example:

     

Rem This is a remark

' This is also a remark

x = 2 * y ' another way to write a remark or comment

You, as a programmer, should decide how much to comment your code.  Consider such factors as reuse, your audience, and the legacy of your code.  In our notes and examples, we try to insert comment statements when necessary to explain some detail.

Strict Type Checking

·         In each assignment statement, it is important that the type of data on both sides of the operator (=) is the same.  That is, if the variable on the left side of the operator is an Integer, the result of the expression on the right side should be Integer. 

·         Visual Basic .NET (by default) will try to do any conversions for you.  Sometimes, however, it ‘guesses’ incorrectly and may provide incorrect or undesired results.  To insure consistency of data types in assignment statements, Visual Basic .NET offers, as an option, strict type checking.  What this means is that your program will not run unless each side of an assignment operator has the same type of data.  With strict type checking, the Intellisense feature of the Code window will identify where there are type inconsistencies and provide suggestions on how to correct the situation.

·         Strict type checking will force you to write good code and eliminate many potential errors.  Because of this, all examples for the remainder of this course will use strict type checking.  To turn on strict type checking, we place a single line of code at the top of each application:

Option Strict On

This line will go right below the Option Explicit On line which forces us to declare each variable we use. ..........

Teach yourself the visual basic .net Language