Adding string binary numbers

Question

My requirement is to add two binary numbers, say "1001" and "0101" as binary1 and binary2.

Partial Class Default2
 Inherits System.Web.UI.Page
 Dim carry As Boolean = False ' Boolean variable to hold the carry if occured
 Protected Sub Button1_Click(sender As Object, e As System.EventArgs) Handles Button1.Click
 Dim binary1 As String = TextBox1.Text 'First binary number
 Dim binary2 As String = TextBox2.Text 'Second binary number
 Dim result As String = "" 'to store the result
 For i As Integer = Len(binary1 ) - 1 To 0 Step -1
 result = bin_add(getbyte(binary1 , i), getbyte(binary1, i)) & result ' calling function
 Next
 If carry = True Then
 result = "1" & result 'if a carry remains add it to the MSB
 End If
 MsgBox(rslt) 'Display the result
 End Sub
 Public Function bin_add(b1 As Boolean, b2 As Boolean) As String'Function which performs the addition of each single bits form the two inputs which is passed from the calling function
 Dim result As Boolean
 If b1 AndAlso b2 = True Then 'both values are 1/true
 If carry = True Then
 result = True
 carry = True
 Else
 result = False
 carry = True
 End If
 ElseIf b1 = False And b2 = False Then 'Both are 0/false
 If carry = True Then
 result = carry
 carry = False
 Else
 result = False
 carry = False
 End If
 Else
 If carry = True Then
 result = False
 carry = True
 Else
 result = True
 carry = False
 End If
 End If
 If result = True Then
 Return "1" 'return 1 for Boolean true
 Else
 Return "0" 'return 0 for Boolean false
 End If
 End Function
 Private Function getbyte(s As String, ByVal place As Integer) As String'Function for getting each individual letters from the input string. i got it from net.
 If place < Len(s) Then
 place = place + 1
 getbyte = Mid(s, place, 1)
 Else
 getbyte = ""
 End If
 End Function
End Class

Notes:

• It gives good results for me only if the no. of digits in both numbers are the same.

Question:

How can I improve the code? Especially, how can I reduce the length of code?

• tim: We don't accept broken code, so I would stick to the first question. But just really quick: prepend the shorter input with enough 0s so that it has the same length (I'm assuming only positive numbers here)
• RubberDuck: I'll refrain from a review, but are you aware that the And Keyword does bitwise addition? Once the binary representation is converted to an integer, this should be trivial.
• Little Master: while evaluating this i got correct answer. i need to shorten the code, and make it workable with all inputs
• JaDogg: @LOsunG make it workable with all inputs -> that's asking others to implement functionality for you, Therefore it is beyond the scope of code review. i need to shorten the code -> This is OK ,because code review is to improve the code.Even though shortening is not always better.

Answer 1

For now, let's ignore the fact that there are easier ways to add binary numbers. There are other issues with this code.

---

Inherits System.Web.UI.Page

Why is code that adds binary numbers inheriting from a UI class? There's no need for this. Separate the concerns and create a module for this code instead.

---

carry is scoped to the class level. This is a symptom of problems in this code.

Protected Sub Button1_Click(sender As Object, e As System.EventArgs) Handles Button1.Click
 Dim binary1 As String = TextBox1.Text 'First binary number
 Dim binary2 As String = TextBox2.Text 'Second binary number
 Dim result As String = "" 'to store the result
 For i As Integer = Len(binary1 ) - 1 To 0 Step -1
 result = bin_add(getbyte(binary1 , i), getbyte(binary1, i)) & result ' calling function
 Next
 If carry = True Then
 result = "1" & result 'if a carry remains add it to the MSB
 End If
 MsgBox(rslt) 'Display the result
End Sub

Getting the values from the UI makes sense, but then you loop over bin_add, which obviously doesn't actually add anything, or you wouldn't need to loop or have a class variable. All of this logic should happen inside of bin_add.

bin_add should take in two strings, handle all of the logic, and return a single string representing the output. While I'm at it, methods should have PascalCased verb-noun names. This method should be called AddBinary and I will refer to it as such for the rest of the review.

As I said earlier, I wouldn't expect a Function that adds binary numbers to take in Boolean values. I would rather it actually take in a byte and overload the method to handle string representation, but I'm lazy and you don't seem to need all that.

Putting it all together, the signature line

Public Function bin_add(b1 As Boolean, b2 As Boolean) As String

Should look like this.

Public Function AddBinary(value1 as String, value2 as String) As String

Implementing this change will be left as an exercise for the reader.

Answer 2

Once the user input is validated to be ones or zeros in the textboxes the conversion / addition is simple. Using the OP's input parameters:

 'verify user input as a binary digit 
 For Each c As Char In TextBox1.Text
 If Not (c = "0"c OrElse c = "1"c) Then
 Stop 'not a binary digit - error handling needed
 Exit Sub
 End If
 Next
 For Each c As Char In TextBox2.Text
 If Not (c = "0"c OrElse c = "1"c) Then
 Stop 'not a binary digit - error handling needed
 Exit Sub
 End If
 Next
 'http://msdn.microsoft.com/en-us/library/1k20k614%28v=vs.110%29.aspx
 Dim num1 As Integer = Convert.ToInt32(TextBox1.Text, 2)
 Dim num2 As Integer = Convert.ToInt32(TextBox2.Text, 2)
 Dim answer As Integer = num1 + num2

One of the overloads to Convert.ToInt32 accepts a base(radix) to be used in the conversion.

• Vogel612: You might want to add, which (by the way absolutely cool) feature of .net you're exploiting, including a link to documentation ;) Additionally you could make the code easier to understand by extracting TextBox1.Text and TextBox2.Text to local variables, but that's yours to decide