error in the final result of extended euclidean code - vb.net

Question

this application for computing the gcd by using extended euclidean but it give me just the value for first iteration but i need the final values of x2 y2 a
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim x1 As Integer
Dim x2 As Integer
Dim y1 As Integer
Dim y2 As Integer
Dim x As Integer
Dim y As Integer
Dim a As Integer
Dim temp As Integer
a = CInt(TextBox1.Text)
Dim b As Integer
b = CInt(TextBox2.Text)
Dim q As Integer
x1 = 0
y1 = 1
x2 = 1
y2 = 0
If b > a Then
temp = a
a = b
b = temp
End If
Do While (b <> 0)
q = Math.Floor(a / b)
a = b
b = a Mod b
x = x2 - q * x1
x2 = x1
y = y2 - q * y1
y2 = y1
x1 = x
y1 = y
Loop
MessageBox.Show("the final value of x2 is " & CStr(x2) & "the final value of y2 is " & CStr(y2) & "the GCD is " & CStr(a), " the result ")
End Sub

Answer 1

Here's your problem:
a = b
b = a Mod b
In the second statement, a is already equal to b, so a Mod b is always zero.

Answer 2

'Euclid's algorithm
'code assumes that you are looking for the GCD of the
'values entered into TextBox1 and TextBox2
Dim dividend As Long
Dim divisor As Long
Dim quotient As Long
Dim remainder As Long
If Long.TryParse(TextBox1.Text, dividend) Then
If Long.TryParse(TextBox2.Text, divisor) Then
'place in correct order
quotient = Math.Max(dividend, divisor) 'determine max number
remainder = Math.Min(dividend, divisor) 'determine min number
dividend = quotient 'max is dividend
divisor = remainder 'min is divisor
Do
quotient = Math.DivRem(dividend, divisor, remainder) 'do the division
'set up for next divide
dividend = divisor 'dividend is previous divisor. if remainder is zero then dividend = GCD
divisor = remainder 'divisor is previous remainder
Loop While remainder <> 0 'loop until the remainder is zero
Label1.Text = dividend.ToString("n0")
End If
End If