#An illustration of functions with parameters and return value.
#The function dist returns the distance between two points whose
#co-ordinates are (x1,y1) and (x2,y2).  The main program (the
#function dist_demo) prompts the user to enter the coordinates
#of two points and prints the distance between them.

#The important thing here is that the dist function can be
#used as a general purpose tool by many other functions:
#It contains no input and output itself, and communicates
#with the function that calls it only through the parameters
#and return values.

def dist(x1,y1,x2,y2):
  xdiff=x1-x2
  ydiff=y1-y2
  return sqrt(xdiff**2+ydiff**2)


def dist_demo():
  a=input("Enter x coordinate of first point")
  b=input("Enter y coordinate of first point")
  c=input("Enter x coordinate of second point")
  d=input("Enter y coordinate of second point")
  print "The distance is "+str(dist(a,b,c,d))