title: How to let python use negative numbers
body: <p>I've been making a linear equation calculator and I'm wondering how to let python use negative numbers. Like int(), float() etc...</p>
  
  <p>here is my code.</p>
  
  <pre><code>import time
  
  print("Hello and welcome to the linear equation calculator.")
  
  time.sleep(2)
  
  print("Enter the first co-ordinate like this - (xx, yy): ")
  coordnte1 = input()
  
  print("Now enter the second co-ordinate like this, with the brackets, - (xx,yy): ")
  coordnte2 = input()
  
  print("Now the y-intercept: ")
  yintrcpt = input()
  
  ydif = coordnte2[1] - coordnte1[1]
  xdif = coordnte2[0] - coodrnte1[0]
  g = ydif / xdif
  
  print("y = " + g + "x + " + yintrcpt)
  </code></pre>
  
  <p>And the problem:</p>
  
  <pre><code>Traceback (most recent call last):
    File "C:/Users/Dale/Documents/GitHub/new_python_rpi_experiments/linear.py", line 17,   in &lt;module&gt;
      ydif = coordnte2[1] - coordnte1[1]
  TypeError: unsupported operand type(s) for -: 'str' and 'str'
  </code></pre>
  
  <p>I'm very new to Python, so any help would be appreciated.</p>