Visual Basic 2015 Lesson 5: Working with Controls

5.1 Text Box

In this lesson, we will learn how to work with some common controls in Visual Basic 2015 . Some of the commonly used controls are label, text box, button, list box, combo box, picture box, timer and more. However, in this lesson, we shall only deal with the text box and the label. The text box is for accepting input from the user as well as to display the output. It can handle string (text) and numeric data but not images or pictures. String in a text box can be converted to a numeric data by using the function Val(text).

Example 5.1

The following program will add the value in text box 1 and value in text box 2 and output the sum in a message box.
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
MsgBox(“The sum is “& Val(TextBox1.Text) + Val(TextBox2.Text))
End Sub

The output window:

Figure 5.1

After clicking Add button, you can get the answer in a message box, as shown in Figure 5.2:

Figure 5.2

5.2 The Label

The label is a very useful control for Visual Basic. It can be used to provide instructions and guides to the users as well as to display outputs. It is different from text box because it can only display static text, which means the user cannot change the text. Using the syntax Label.Text, it can display text and numeric data . You can change its text in the properties window and also at runtime.

Example 5.2

In this program, instead of showing the sum in a message box, we wish to display the sum on a label.This  a simple calculator program that can calculates the sum of two numbers entered by the user. To design the interface,  you add two text boxes, three labels  and a button on the form. Under the respective properties windows, change the name of the first text box to txtNum1 and the name of second text box to txtNum2. Next, change the text of first label to + , the text of the second label to = . For the third label, change the autosize property to false and the name to LblAns. Drag the third label to appropriate size and set its background to yellow colour. For the button, change its name to BtnCal and its text to Calculate.  Lastly, change the text of the form to Simple Calculator. The two text boxes are used to accept inputs from the user . The button is  programmed to calculate the sum of the two numbers using the plus operator.
The Code
Public Class Form1
Private Sub BtnCal_Click(sender As Object, e As EventArgs) Handles BtnCal.Click
Dim num1 As Single = Val(TxtNum1.Text)
Dim num2 As Single = Val(TxtNum2.Text)
Dim Sum As Single = num1 + num2
LblAns.Text = Sum.ToString
End Sub
End Class
The Dim keyword is to declare a number  as a single precision number and the function Val is to convert a string to a number. The method ToString is to display an output as string. We shall learn more about Dim in later lesson.
The output window:

Figure 5.3