Controling Program Flow

In previous lessons, we have learned how to create Visual Basic code that can accept input from the user and display the output without controlling the program flow. In this chapter, you will learn how to crreate VB code that can make decision when it process input from the user, and control the program flow in the process. Decision making process is an important part of programming because it can help to solve practical problems intelligently so that it can provide useful output or feedback to the user. For example, we can write a program that can ask the computer to perform certain task until a certain condition is met.

7.1 Conditional Operators

To control the VB program flow, we can use various conditional operators.

Working With Variables

6.1 Assigning Values to Variables
After declaring various variables using the Dim statements, we can assign values to those variables. The general format of an assignment is Variable=Expression The variable can be a declared variable or a control property value. The expression could be a mathematical expression, a number, a string, a Boolean value (true or false) and more. The following are some examples: 

firstNumber =100
secondNumber =firstNumber-99
userName ="John Lyan"
userpass.Text = password
Label1.Visible = True
Command1.Visible = false
Label4.Caption = textbox1.Text
ThirdNumber = Val(usernum1.Text)
total = firstNumber + secondNumber+ThirdNumber 

Managing Visual Basic Data

There are many types of data that we come across in our daily life. For example, we need to handle data such as names, addresses, money, date, stock quotes, statistics and more everyday. Similarly in Visual Basic, we have to deal with all sorts of of data, some can be mathematically calculated while some are in the form of text or other forms. VB divides data into different types so that it is easier to manage when we need to write the code involving those data.

5.1 Visual Basic Data Types
Visual Basic classifies the information mentioned above into two major data types, they are the numeric data types and the non-numeric data types.

5.1.1 Numeric Data Types
Numeric data types are types of data that consist of numbers, which can be computed mathematically with various standard operators such as add, minus, multiply, divide and more. Examples of numeric data types are examination marks, height, weight, the number of students in a class, share values, price of goods, monthly bills, fees and others. In Visual Basic, numeric data are divided into 7 types,

Writing the Code

Each control or object in VB can usually run many kinds of events or procedures; these events are listed in the dropdown list in the code window  that is displayed when you double-click on an object and click on the procedures’ box(refer to Figure 2.3). Among the events are loading a form, clicking of a command button, pressing a key on the keyboard or dragging an object and more. For each event, you need to write an event procedure so that it can perform  an action or a series of actions

To start writing an event procedure, you need to double-click an object. For example, if you want to write an event procedure when a user clicks   a command button, you double-click on the command button and an event procedure will appear as shown in Figure 2.1. It takes the following format: 

Private Sub Command1_Click

(Key in your program code here)

End Sub