COMPSCI 101 Principles of Programming

1. COMPSCI 101Principles of Programming Lecture 24 Random Numbers, User Input and While Loops Dr. Patricia J. Riddle

2. Learning outcomes • At the end of this lecture, students should be able to: • Use random number generator • Use while loops • Get user input from the keyboard COMPSCI 101 - Principles of Programming

3. Review random.randint(1,8) • Returns a random integer between 1 and 8 (inclusive) • Must import the random module COMPSCI 101 - Principles of Programming

4. User Input • input([prompt]) • Displays prompt (if given) and reads a line from keyboard • Returns the line as a string, e.g. • name = input("What is your name? ") • If you want to read numbers, convert the string into a number using int or float as appropriate, e.g. • age_as_string = input("How old are you? ") • age = int(age_as_string) • Or • weight = float(input("What's your weight in kg? ")) COMPSCI 101 - Principles of Programming

5. While Loop • The for loop iterates over a known sequence. • Sometimes we don’t have a known sequence, e.g. • “Stir until boiling” • “Keep reading input until the user types quit” • “Keep refining the answer until it’s good enough” • Situations like this need a different sort of loop: • The while loop COMPSCI 101 - Principles of Programming

6. While Example • If a population of bacteria increases in size by 21% every minute, how long does it take for the population size to double? minutes = 0 population = 1000 growth_rate = 0.21 while population < 2000: population *= (1 + growth_rate) minutes += 1 print(minutes, " minutes required.") print("Population =", int(population)) COMPSCI 101 - Principles of Programming

7. Exercise • Write a program that calls a function function named play_rock_paper() that plays rock paper scissors with the user. User input must be from the keyboard. Example of Game: Choose "r" "p" or "s": r Computer chose rock. You chose rock. We are tied. Do you want to play again? Answer "y" or "n": y Choose "r" "p" or "s": s Computer chose rock. You chose scissors. Computer wins. Do you want to play again? Answer "y" or "n": y Choose "r" "p" or "s": p Computer chose rock. You chose paper. You win. COMPSCI 101 - Principles of Programming

8. Answer COMPSCI 101 - Principles of Programming

9. Helper Function • “who_wins” helper function from Slide 5 in Lecture 21 COMPSCI 101 - Principles of Programming

10. More Nested Loop Practice COMPSCI 101 - Principles of Programming

11. Exercise • Write a function named test_sudoku()that accepts a list specifying the sudoku board and and returns True if the board is a legal sudoku board and False otherwise. 0 represents an empty cell in the board. Sudoku is a logic-based, combinatorial number-placement puzzle. The objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 sub-grids that compose the grid (also called "boxes", "blocks", "regions", or "sub-squares") contains all of the digits from 1 to 9. The puzzle setter provides a partially completed grid, which for a well-posed puzzle has a unique solution. Wikipedia >>> test_sudoku([5, 9, 8, 2, 7, 4, 1, 3, 6, 3, 2, 4, 9, 1, 6, 8, 5, 7, 1, 7, 6, 5, 8, 3, 2, 9, 4, 9, 8, 5, 3, 2, 7, 6, 4, 1, 7, 1, 2, 4, 6, 5, 3, 8, 9, 4, 6, 3, 8, 9, 1, 5, 7, 2, 6, 4, 1, 7, 5, 8, 9, 2, 3, 2, 5, 7, 1, 3, 9, 4, 6, 8, 8, 3, 9, 6, 4, 2, 7, 1, 5]) True >>> test_sudoku([5, 5, 8, 2, 7, 4, 1, 3, 6, 3, 2, 4, 9, 1, 6, 8, 5, 7, 1, 7, 6, 5, 8, 3, 2, 9, 4 , 9, 8, 5, 3, 2, 7, 6, 4, 1, 7, 1, 2, 4, 6, 5, 3, 8, 9, 4, 6, 3, 8, 9, 1, 5, 7, 2, 6, 4, 1, 7, 5, 8, 9, 2, 3, 2, 5, 7, 1, 3, 9, 4, 6, 8, 8, 3, 9, 6, 4, 2, 7, 1, 5]) False COMPSCI 101 - Principles of Programming

12. Suduko Example COMPSCI 101 - Principles of Programming

13. Answer COMPSCI 101 - Principles of Programming

14. Helper Functions COMPSCI 101 - Principles of Programming

15. Summary • While loops • User input • Random number generation COMPSCI 101 - Principles of Programming

16. Next Tuesday • Dictionaries COMPSCI 101 - Principles of Programming