title: Integer to String error in my program
body: <p>I am having a problem with a program I am currently working on. It is a GTIN-8 Code generator. When I try to start the program, I get the error:</p>
  
  <pre><code>Type Error: Can't convert 'int' to str implicitly.
  </code></pre>
  
  <p>My code is as follows:</p>
  
  <pre><code>sevenNum = ""
  gtinNum = ""
  checkDigit = ""
  total = ""
  
  a = ""
  b = ""
  c = ""
  d = ""
  e = ""
  f = ""
  g = ""
  
  def GTINCalc():
      a = int(sevenNum[0])*3
      b = int(sevenNum[1])*1
      c = int(sevenNum[0])*3
      d = int(sevenNum[1])*1
      e = int(sevenNum[0])*3
      f = int(sevenNum[1])*1
      g = int(sevenNum[0])*3
  
      total = (a+b+c+d+e+f+g)
  
      checkDigit = (total + 9) // 10 * 10 - total
  
      print("GTIN-8 Code:" + a+b+c+d+e+f+g+checkDigit)
  
  
  def sevenNumAsk():
      sevenNum = input("Enter a 7 digit number to be converted into a GTIN-8 Number")
  if sevenNum.isdigit() == True and len(sevenNum) == 7:
      print("Valid Number - Calculating GTIN-8...")
      GTINCalc()
  else:
      print("The number is not valid - please re-enter ")
      sevenNumAsk()
  
  sevenNumAsk()
  </code></pre>
  
  <p>I am having problems with this part:</p>
  
  <pre><code>total = (a+b+c+d+e+f+g)
  
  checkDigit = (total + 9) // 10 * 10 - total
  </code></pre>
  
  <p>Many thanks.</p>