COMPSCI 101 Principles of Programming

1. COMPSCI 101Principles of Programming Lecture 20 – Boolean Operators Dr. Patricia J. Riddle

2. Learning outcomes • At the end of this lecture, students should be able to: • Use and, or and not in conditional conditions • Understand basic truth tables • Use short circuit evaluation COMPSCI 101 - Principles of Programming

3. Review of Booleans • Booleans represent truth values • True • False • Relational operators compare two different things • Evaluate to Boolean values • == • < • <= • > • >= • != COMPSCI 101 - Principles of Programming

4. Boolean Operator Examples • Boolean Operators are and, or and not: if palindrome("word") if not palindrome("word") if palindrome("word") and heterogram("word") if palindrome("word") or heterogram("word") COMPSCI 101 - Principles of Programming

5. Boolean Operator Truth Tables COMPSCI 101 - Principles of Programming

6. Exercise • Write a function named is_a_leap_year() that accepts a year as a parameter and returns True if the year is a leap year and False otherwise. • A year is a leap year if it is divisible by 400, or divisible by 4 but not by 100. COMPSCI 101 - Principles of Programming

7. Original Leap Year Code • From lecture 12, slide 19 defis_leap_year(year): if year % 400 == 0: return True elifyear % 100 == 0: return False elifyear % 4 == 0: return True else: return False COMPSCI 101 - Principles of Programming

8. Answer defis_a_leap_year(year): if not isinstance(year,int): print("year is not an integer") return False if (year % 400) == 0 or ((year % 4) == 0 and (year % 100) != 0): return True return False COMPSCI 101 - Principles of Programming

9. Short Circuit Evaluation • If A and B • B is not evaluated unless A is True • If A or B • B is not evaluated unless A is False • Examples If divisor != 0 and numerator/divisor > 4: If divisor = 0 or numerator/divisor > 4: COMPSCI 101 - Principles of Programming

10. Exercise • Write a function named find_names_with() that accepts a letter, a location and a list of names, and returns the list of names that have the letter in the specified location. find_names_with("r", 3, ["Sara","Fred","Al","Tar"]) ['Sara', 'Tar'] COMPSCI 101 - Principles of Programming

11. Answer deffind_names_with(letter, place, names_list): name_list = [] for name in names_list: if len(name) >= place and name[place-1] == letter: name_list += [name] return name_list COMPSCI 101 - Principles of Programming

12. Exercise • Write a function named pangram() that accepts a string parameter and returns True if the string is a pangram and False otherwise. • A pangram is a sentence which contains every letter in the alphabet. “The quick brown fox jumps over the lazy dog” Perfect panagrams “TV quiz jock, Mr. PhD, bags few lynx” “Glum Schwartzkopfvex'd by NJ IQ” “Blowzy night-frumps vex'd Jack Q” COMPSCI 101 - Principles of Programming

13. Answer defpangram(sentence): if not isinstance(sentence,str): print("sentence is not a string") return False alphabet = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"] for letter in alphabet: if letter not in sentence: return False return True COMPSCI 101 - Principles of Programming

14. Exercise • Write a function named pangram2() that accepts a string parameter and returns True if it is a Pangram and False otherwise, and works for both uppercase and lowercase letters Perfect panagrams “TV quiz jock, Mr. PhD, bags few lynx” “Glum Schwartzkopfvex'd by NJ IQ” “Blowzy night-frumps vex'd Jack Q” COMPSCI 101 - Principles of Programming

15. Answer def pangram2(sentence): if not isinstance(sentence,str): print("sentence is not a string") return False alphabet = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"] capital_alphabet = ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y”, "Z"] alphabet_range = range(0,len(alphabet)) for index in alphabet_range: if alphabet[index] not in sentence and capital_alphabet[index] not in sentence: return False return True COMPSCI 101 - Principles of Programming

16. The Game of Life http://en.wikipedia.org/wiki/Conway%27s_Game_of_Life The universe of the Game of Life is an infinite two-dimensional orthogonal grid of square cells, each of which is in one of two possible states, alive or dead. Every cell interacts with its 8neighbours, which are the cells that are horizontally, vertically, or diagonally adjacent. At each step in time, the following transitions occur: • Any live cell with fewer than two live neighbours dies, as if caused by under-population. • Any live cell with two or three live neighbours lives on to the next generation. • Any live cell with more than three live neighbours dies, as if by overcrowding. • Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction. • Wikipedia COMPSCI 101 - Principles of Programming

17. Exercise • Write a function named is_alive() that accepts 2 parameters: a Boolean value (alive) and a number between 1 and 8 (live_neighbours) and returns True if the cell should turn on and False otherwise >>> is_alive(True,1) False >>> is_alive(True,3) True >>> is_alive(False,3) True >>> is_alive(False,4) False COMPSCI 101 - Principles of Programming

18. Answer • Nested if statements can be hard to read defis_alive(alive,neighbours_alive): if alive: if neighbours_alive < 2: return False if neighbours_alive > 3: return False return True if neighbours_alive== 3: return True return False COMPSCI 101 - Principles of Programming

19. Answer defis_alive2(alive,neighbours_alive): its_dead = False its_alive = True if alive and (neighbours_alive < 2 or neighbours_alive> 3): return its_dead if not alive and neighbours_alive!= 3: return its_dead return its_alive COMPSCI 101 - Principles of Programming

20. Summary • Basic Truth tables • and • or • not • Use of Complex conditions: • Use of “and”, “not”, and “or” • Benefits of Short Circuit evaluation: • Allows you to write code that will not trigger error messages COMPSCI 101 - Principles of Programming

21. Tomorrow • Complex String Processing COMPSCI 101 - Principles of Programming