In this lesson, we shall learn how to create a Function in Visual Basic 2017. A function is similar to a sub procedure, however, there is one major difference. A function returns a value whilst a sub procedure does not. In Visual Basic 2017, there are two types of functions, the built-in functions and the user-defined functions.

To create a user- defined function in Visual Basic 2015, you can use the following syntaxes:

Public Function functionName (Argument As dataType,..........) As dataType

or

Private Function functionName (Argument As dataType,..........) As dataType

The keyword Public indicates that the function is applicable to the whole project and the keyword Private indicates that the function is only applicable to a certain module or procedure. An argument is a parameter that can pass a value back to the function.There is no limit to the number of arguments you can put in.

This BMI calculator is a Visual Basic 2017 program that can calculate the body mass index of a person based on his or her body weight in kilogram and the body height in meter. BMI can be calculated using the formula weight/( height )^{2}, where weight is measured in kg and height in meter.

If the BMI is more than 30, a person is considered obese. You can refer to the following range of BMI values for your weight status.

- Underweight = <18.5
- Normal weight = 18.5-24.9
- Overweight = 25-29.9
- Obesity = BMI of 30 or greater

Public Class Form1 Private Function BMI(Height As Single, weight As Single) As Double BMI = weight / Height ^ 2 End Function Private Sub BtnCal_Click(sender As Object, e As EventArgs) Handles BtnCal.Click Dim h As Single, w As Single h = Val(TextBox1.Text) w = Val(TextBox2.Text) LblBMI.Text = BMI(h, w) End Sub End Class

The concept of future value is related to time value of money. If you deposit your money in a bank as a savings account or a fixed deposit account for a certain period of time, you will earn a certain amount of money based on the compound interest computed periodically, and this amount is added to the principal if you continue to keep the money in the bank. Interest for the following period is computed based on the initial principal plus the interest, this amount becomes the new principal. Subsequent interests are computed in the same manner.

For example, let's say you deposit $1000 in a bank and the bank is paying you 5% compound interest annually. After the first year, you will earn an interest of $1000x0.05=$50. The new principal will be $1000+$1000x0.05=$1000(1+0.05)=$1000(1.05)=$1050. After the second year, the new principal is $1000(1.05)x1.05=$1000(1.05)2 =$1102.50. This new principal is called the future value.

Following the above calculation, the future value after n years will be

FV = PV * (1 + i / 100)^{n}

Where PV represents the present value, FV represents the future value, i is the interest rate and n is the number of periods (Normally months or years).

Public Class Form1 Private Function FV(pv As Single, i As Single, n As Integer) As Double FV = pv * (1 + i / 100) ^ n End Function Private Sub BtnCal_Click(sender As Object, e As EventArgs) Handles BtnCal.Click Dim FutureVal As Single Dim PresentVal As Single Dim interest As Single Dim period As Integer PresentVal = TxtPV.Text interest = TxtInt.Text period = TxtN.Text FutureVal = FV(PresentVal, interest, period) LblFV.Text = Format(FutureVal, "$#,##0.00") End Sub End Class

Public Class Form1 Private Function sqroot(ByRef x As Single) As Double x = x ^ 0.5 sqroot = x End Function Private Function sqroot1(ByVal y As Single) As Double y = y ^ 0.5 sqroot1 = y End Function Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim u As Single u = 9 MsgBox(3 * sqroot(u), , "ByRef") MsgBox("Value of u is " & u, , "ByRef") End Sub Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click Dim u As Single u = 9 MsgBox(3 * sqroot1(u), , "ByVal") MsgBox("Value of u is " & u, , "ByVal") End Sub End Class

Notice that the value of u has been changed to 3

Notice that the value of u remains unchanged.

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