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 import random defplay_rock_paper(): mapping2 = ["paper","scissors","rock"] again = "y" while again == "y": computer_num = random.randint(0,2) person2_choice = input('Choose "r" "p" or "s": ') person2_num = find_mapping(person2_choice) print("Computer chose " + mapping2[computer_num] +".") print("You chose " + mapping2[person2_num] + ".") winner = who_wins(mapping2[computer_num],mapping2[person2_num]) if winner == "person2": print("You win.") elif winner == "tie": print("We are tied.") else: print("Computer wins.") again = input('Do you want to play again? Answer "y" or "n": ') play_rock_paper() COMPSCI 101 - Principles of Programming

9. Helper Function • “who_wins” helper function from Slide 5 in Lecture 21 defwho_wins(person1_choice,person2_choice): if (person1_choice == "rock" and person2_choice == "scissors") or (person1_choice == "scissors" and person2_choice == "paper") or (person1_choice == "paper" and person2_choice == "rock"): return "person1" if person1_choice == person2_choice: return "tie" return "person2” deffind_mapping(person_choice): mapping = ["p","s","r"] for i in range(0,3): if person_choice == mapping[i]: return i 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 deftest_sudoku(board): for i in range(0,9): col = board[i:len(board):9] if not test(col): return False row = board[i*9:(i*9)+9] if not test(row): return False for column in range(0,3): for row in range(0,3): start_square = column*3+row*9*3 square = make_square(start_square, board) if not test(square): return False return True COMPSCI 101 - Principles of Programming

14. Helper Functions deftest(my_list): for i in range(0,9): if my_list[i] != 0 and my_list[i] in my_list[i+1:]: return False return True defmake_square(start,board): square = [] for row in range(0,3): for col in range(0,3): square += [board[start + (row * 9) + col]] return square 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