Welcome to CS

Let’s use what we have learned about random numbers and if statements to build a simulation. We want to know the answer to “If you flip a coin 100 times, what are the chances you get 5 heads in a row at some point?”

This is a complex problem. We need to flip a coin 100 times and figure out if we get at least 5 heads in a row - that is slightly different than what we have done so far. We will also need to repeat that a bunch of times - if we want to know the chances of something happening, we will need to do it say 10,000 times and see what percent of the time we get the right result.

So let’s start with the basics - how do we see if we got 5 heads in a row? Well, each time we flip a coin, if it is a head, we need to add one to headsInARow. If it is a tail, that means we now have seen 0 headsInARow:

Try running the program. Does it appear to work correctly? Once you have verified that the code appears to work, we need to modify it so it produces just one answer - true or false - yes we got at least 5 heads in a row or no we did not.

To do this, we will use break to stop the loop if we see 5 heads in a row. The break command is a way to stop a loop - it “breaks” us out of the loop and continues with the rest of the program. In this case, if headsInARow hits 5, we can stop the loop early - we know that we got 5 heads and we don’t want to keep going and flip a tail and then “forget” that we had 5 in a row.

Now, we want to turn the code into a function that returns True or False instead of printing the answer. Making it into a function will make it easier to repeat the process over and over.

def checkHeadsInRow(desiredStreak):
 headsInARow = 0 #start with 0
---
 for i in range(100):
---
  flip = random.randrange(0, 2)
---
  if flip == 0:
   headsInARow = headsInARow + 1
  else:
   headsInARow = 0
---
  if headsInARow == desiredStreak:
   break
---
 # Make final decision
 if headsInARow >= desiredStreak:
---
  return True
---
 else:
---
  return False