Arraylist.Contains Doesn't Return True VB.NET - vb.net

Question

comps.Contains doesn't return TRUE even though comps contains it.
I debugged it step by step and I can't see where the problem is.
By the way the purpose of the code is to show the pairs that sum up to SUM value. (If the sum is 5 and theres 1 and 4 then the code should return 1 and 4)
Public Function getPairs(ByVal array As ArrayList, ByVal sum As Integer)
Dim comps, pairs As New ArrayList
For index = 0 To array.Count - 1
If (comps.Contains(array(index)) = True) Then
pairs.Add(array(index))
Else
comps.Add(sum - array(index))
End If
Next
Return pairs
End Function
Sub Main()
' 1,3,2,5,46,6,7,4
' k = 5
'Dim arraylist As New ArrayList()
Console.Write("Enter your array :")
Dim arraylist As New ArrayList
arraylist.AddRange(Console.ReadLine().Split(","))
Console.Write("Enter the sum:")
Dim sum As Integer = Console.ReadLine()
getPairs(arraylist, sum)
Console.ReadKey()
End Sub

Answer 1

The ArrayList you populate from user input contains strings (results from splitting the user input string). The comps ArrayList contains integers (results from subtraction). When it tries to find the string "2" in the ArrayList that contains a 2, it fails.
You should convert your user input to integers so that you are comparing the same data types.

Answer 2

First, turn on Option Strict. Tools Menu -> Options -> Projects and Solutions -> VB Defaults. This will point out problems with your code and help you to avoid runtime errors.
ArrayList is not used much in new code but is around for backward compatibility. List(Of T) is a better choice for new code.
Module Module1
Sub Main()
' 1,3,2,5,46,6,7,4
' k = 5
'Dim arraylist As New ArrayList()
Console.Write("Enter your array :")
Dim arraylist As New ArrayList
'Option Strict would not allow this line to compile
'.Split takes a Char, the same c tells the compiler that "," is a Char
arraylist.AddRange(Console.ReadLine().Split(","c))
Console.Write("Enter the sum:")
'Option Strict would not allow a string to be dumped into an integer
Dim sum As Integer
Dim Pairs As New ArrayList
If Integer.TryParse(Console.ReadLine, sum) Then
'Your Function returns an array list but you
'throw it away by not setting up a variable to receive it
Pairs = getPairs(arraylist, sum)
Else
Console.WriteLine("Program aborted. Sum was not a number.")
End If
For Each item In Pairs
Console.WriteLine(item)
Next
Console.ReadKey()
End Sub
'Functions need a return data type in the declaration
Public Function getPairs(ByVal array As ArrayList, ByVal sum As Integer) As ArrayList
Dim comps, pairs As New ArrayList
For index = 0 To array.Count - 1
'I don't see how this can ever be true since comps is empty
If comps.Contains(array(index)) Then 'Since .Contains returns a Boolean, no = True is necessary
pairs.Add(array(index))
Else
'Ideally each item in array should be tested to see if it is a number
'You will get an exception if CInt fails
comps.Add(sum - CInt(array(index)))
'You never use the comps ArrayList
End If
Next
'The pairs ArrayList is empty
Return pairs
End Function
End Module
I don't see how this code could accomplish what you describe as your goal. I think you should start again. Talk through how you would accomplish your task. Then write it out on paper, not in code. Then you will see more clearly how to code your project.

Answer 3

The big problem is the original code is this line:
Dim comps, pairs As New ArrayList
That code creates two ArrayList reference variables, but only one ArrayList object. comps remains null/Nothing.
But beyond that, the ArrayList type has been dead since .Net 2.0 came out back in 2005... more than 10 years now. It only exists today for backwards compatibility with old code. Don't use it!
This is better practice, especially in conjunction with Option Strict and Option Infer:
Public Function getPairs(ByVal items As IEnumerable(Of Integer), ByVal sum As Integer) As IEnumerable(Of Integer)
Dim comps As New HashSet(Of Integer)()
Dim result As New List(Of Integer)()
For Each item As Integer In items
If Not comps.Add(item) Then
result.Add(sum - item)
End If
Next
Return result
End Function
Sub Main()
Console.Write("Enter your array: ")
Dim input As String = Console.ReadLine()
Dim list As List(Of Integer) = input.Split(",").Select(Function(item) CInt(item)).ToList()
Console.Write("Enter the sum: ")
Dim sum As Integer = CInt(Console.ReadLine())
Dim pairs = getPairs(list, sum).Select(Function(s) s.ToString())
Console.WriteLine("Pairs are: {0}", String.Join(", " pairs))
Console.ReadKey()
End Sub