1. COSC 1306—COMPUTER SCIENCE AND PROGRAMMING PYTHON BRANCHES AND LOOPS Jehan-François Pâris jfparis@uh.edu

2. STARTING WITH A GAME

3. Number guessing game We use a random number generator to generate a random number between 1 and 10 Users are asked to guess the number until they come with the right value

4. Number guessing game We use a random number generator to generate a random number between 1 and 10 Users are asked to guess the number until they come with the right value

5. Flow chart Generate RN n You win Input i i == n TrueFalse

6. More about flow charts Graphic representation of flow of control –Loops represented by loops –Ifs have two branches ??? False True

7. Simple if If condition : something If tank_empty : get_gas condition False True something

8. FalseTrue If with else clause (I) If condition: something else: other stuff other stuff something condition

9. If with else clause (II) If hungry : Macdonald else : Starbucks In either case, you will leave the freeway

10. While something True False while condition : something while stain : keep_washing condition Go back!

11. How to generate RN Import a function from module random – from random import randint randint(min, max) –generates an integer between min and max

12. The program (I) # guess.py “”” must guess a random number between 1 and 10 “”” # secret # guess

13. The program (II) from random import randint secret = randint (1,10) guess = -1 # bad guess while guess != secret : guess = int(input("Enter your guess: ") print("You win!")

14. A better program Tells whether guess is too low or too high Must consider three cases inside the loop –Correct guess –Guess that is too low –Guess that is too high

15. The better program (I) # guess.py “”” must guess a random number between 1 and 10 “”” # secret # guess from random import randint secret = randint (1,10) guess = -1 # bad guess

16. The program (II) while guess != secret : guess = int(input(“Enter your guess: “)) if guess == secret : print ("You win!") else : if guess < secret : print ("Too low!") else: print ("Too high!")

17. Using an elif (I) Too many nested ifs if cond-1 : … else if cond-2 : … else if cond-3 : … else …

18. Example while guess != secret : guess = int(input("Enter your guess: ")) if guess == secret : print ("You win!") elif guess < secret : # observe indentation print ("Too low!") else: print ("Too high!")

19. Using an elif (II) With elif, lines align better if cond-1 : … elif cond-2 : … elif cond-3 : … else …

20. Indenting advice Python attaches great importance to indenting –You cannot indent anything that is not inside An if, a while, a for, … A function declaration or a main function –Your indentation must be consistent Do not mix spaces and tabs