Multiplying, subtracting and dividing binary numbers give wrong answers - swift

Question

I'm making a binary calculator app.
No buildtime issues but in the app only adding binary numbers give the right answer, multiplying, subtracting and dividing don't.
Dividing - every answer = 1 (1010-0001 = 1; 10101010-1010 = 1)
Multiplying - every answer is wrong, (11111 x 101010 = 1111000001, should be 10100010110)
Subtracting - every answer = 0 ( 1010-0001 = 0; 1010101-0001 = 0)
I tried making the code more explanatory and it worked in the playground (ending with print() ) but when I changed the apps code, the answers were the same.
var numberOnScreen:Int = 0;
var previousNumber:Int = 0;
var doingMath = false
var operation = 0;
var decimal = 0;
var decimal1 = 0;
var binary:String = ""
var binary1:String = ""
#IBOutlet weak var label: UILabel!
#IBAction func Numbers(_ sender: UIButton) {
if doingMath == true
{
label.text = String(sender.tag-1)
numberOnScreen = Int(label.text!)!
doingMath = false
}
else
{
label.text = label.text! + String(sender.tag-1)
numberOnScreen = Int(label.text!)!
}
}
#IBAction func buttons(_ sender: UIButton) {
if label.text != "" && sender.tag != 6 && sender.tag != 8
{
previousNumber = Int(label.text!)!
binary = "\(previousNumber)"
decimal = Int(binary, radix: 2)!
binary1 = "\(numberOnScreen)"
decimal1 = Int(binary1, radix: 2)!
operation = sender.tag
doingMath = true;
}
else if sender.tag == 8
{
if operation == 3 //adding
{
label.text = String((decimal + decimal1), radix: 2)
}
else if operation == 4 //subtracting
{
label.text = String((decimal - decimal1), radix: 2)
}
else if operation == 5 //multiplying
{
label.text = String((decimal * decimal1), radix: 2)
}
else if operation == 7 //dividing
{
label.text = String((decimal / decimal1), radix: 2)
}