title: Adding binary numbers Python
body: <p>I'm trying to add two binary numbers in python using a simple code. Can someone tell me why this isn't working? Thanks so much! I tried breaking the code down but when I break it down it all works separately. But of course when I put it together it doesn't work.</p>
  
  <p>I'm a beginner in Python so explanations will certainly be appreciated. Thanks for the help!</p>
  
  <pre><code>#Enter numbers and define variables
  number1=input("Enter 1st Binary Number:")
  number2=input("Enter 2nd Binary Number:")
  x1 = number1[0]
  x2 = number1[1]
  y1 = number2[0]
  y2 = number2[1]
  
  #Convert to integers from strings
  int(x1)
  int(x2)
  int(y1)
  int(y2)
  
  
  
  #Digit 1 of answer and digit to be carried
  if x1+y1==0:
    a1 = 0
    c1 = 0
  if x1+y1==1:
    a1 = 1
    c1 = 0
  if x1+y1==2:
    a1 = 0
    c1 = 1
  
  
  
  
  #Digit 2 of answer and digit to be carried
  if x2+y2+c1==0:
    a2=0
    c2=0
  if x2+y2+c1==1:
    a2=1
    c2=0
  if x2+y2+c1==2:
    a2=0
    c2=1
  if x2+y2+c1==3:
    a2=1
    c2=1
  
  #Digit 3 of answer
  c2=a3
  
  if a3==1:
    print ("a3" + "a2" + "a1")
  
  if a3==0:
    print ("a2" + "a1")
  </code></pre>
  
  <p>The error it's giving is that c1 and a1 aren't defined.</p>
  
  <p>Thanks again!</p>