Sum of Numbers with LOOPING - vb.net

Question

So for my class I am trying to do write a code that sums up numbers from 1-10. For example if a user puts in 3, the that program will add 1+2+3 and the final answer would be 6.......I am trying to do this using looping and also with a display mesage that gives the answer.
this is the code I have so far........
Option Strict On
Public Class frmSumOfNumbers
Private Sub btnEnterNumbers_Click(sender As Object, e As EventArgs) Handles btnEnterNumbers.Click
'For loop from 0 to counter -1
InputBox("Enter A Positive integer value", "Input needed", "10")
End Sub
Function Validation(ByVal PositiveNumber As Double, ByRef Result As Double) As Boolean
If PositiveNumber > -1 Then
Result = CDbl(PositiveNumber)
Else
'pop message box and return false if not positive
MessageBox.Show("Please enter positive numbers only")
Return False
End If
End Function
Private Sub btnExit_Click(sender As Object, e As EventArgs) Handles btnExit.Click
' Closes the program
Close()
End Sub
End Class

Answer 1

Your first problem is providing a place to collect the input values from the user. Take a look at the InputBox Function https://learn.microsoft.com/en-us/dotnet/api/microsoft.visualbasic.interaction.inputbox?view=netframework-4.8
Notice that is returns a string. We can get the input from the user by providing a String variable.
Dim UserInput As String
UserInput = InputBox("Enter A Positive integer value", "Input needed", "10")
But this value will disappear as soon as we reach End Sub! If we use a form level variable to collect the values the variable will be around as long as the form is open. Another advantage of a form level (class level) variable is that it can be seem by any method in the from.
We can use a collection variable like an array or a list. Since we are not sure how many numbers the user will enter let's use a list. With an array we would have to use ReDim Preserve every time we got a new number to resize the array. That isn't necessary with a list. See https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1?view=netcore-3.1
At the Form level...
Private IntegerList as New List(Of Integer)
But the we have a String variable from the user. This is where your validation code comes in. We need to pass the what the user entered in the input box (remember InputBox returns a String) so the datatype of the argument in String. We want to get back an Integer so the datatype of the Function is Integer. Any return statement in the function must be followed by an Integer value.
I used Integer.TryParse to test if the input was a number and then I tested to see if the number is positive. See the docs https://learn.microsoft.com/en-us/dotnet/api/system.int32.tryparse?view=netcore-3.1
If the user input passes the validation then the number is added to the list, otherwise the message is displayed.
To add up the list you can the .Net framework do the loop behind the scenes with the .Sum method of a list or you can use a For Each loop to do it yourself. Same result.
Private IntegerList As New List(Of Integer)
Private Sub AddANumber_Click(sender As Object, e As EventArgs) Handles AddANumber.Click
Dim UserInput = InputBox("Enter A Positive integer value", "Input needed", "10")
Dim RetVal = Validation(UserInput)
If RetVal > -1 Then
IntegerList.Add(RetVal)
Else
MessageBox.Show("Please enter positive numbers only")
End If
End Sub
Function Validation(ByVal UserInput As String) As Integer
Dim ReturnInteger As Integer
If Integer.TryParse(UserInput, ReturnInteger) AndAlso ReturnInteger > -1 Then
Return ReturnInteger
Else
Return -1
End If
End Function
Private Sub DisplayTotal_Click(sender As Object, e As EventArgs) Handles DisplayTotal.Click
Dim Total = IntegerList.Sum
MessageBox.Show($"The Total is {Total}")
Dim LoopTotal As Integer
For Each i In IntegerList
LoopTotal += i
Next
MessageBox.Show($"The LoopTotal is {LoopTotal}")
End Sub
Note: The strings preceded by a $ are called interpolated strings. You can search for that term to learn how they work.