1. Lecture 20 – Test revision COMPSCI 101 Principles of Programming

2.  Naming conventions  Python types  Variables  Strings  Operators  Algebraic expressions  The math module, the random module  Getting input from the user  Functions  Boolean expressions, selection statements  Loops – while and for…in  Lists Test topics CompSci 101 - Principles of Programming2

3. Variable names  Must begin with a letter or underscore, e.g., number1 is OK, but 1number is not  May contain letters, digits, and underscores, e.g., this_is_an_identifier_123  May be of any length  Upper and lower case letters are different, e.g., Rope_Length is not the same variable as rope_length  The standard way for most things named in python is lower case with separate words joined by an underline, e.g., my_list x age age_of_child box1 box_2 _age age_ x age age_of_child box1 box_2 _age age_ 3 age of child age-child 1st 2_box 3 age of child age-child 1st 2_box valid variable names: NOT valid variable names: CompSci 101 - Principles of Programming3

4. Python types encountered this semester  Information in a program is categorised into different types. A type in Python defines two things: the internal structure of the type (the information being stored) the kinds of operations you can perform with this type of object int float string boolean list CompSci 101 - Principles of Programming4

5. Converting between types  Some types can be converted into different types: result1 = int("2.1") result2 = float("2.1 ") input = "2.1" result3 = "$" + float(input) result1 = int("2.1") result2 = float("2.1 ") input = "2.1" result3 = "$" + float(input) result1 = float("2.1") result2 = int("24") result3 = float("24") input = "2.1" result4 = "$" + str(float(input) * 2) result1 = float("2.1") result2 = int("24") result3 = float("24") input = "2.1" result4 = "$" + str(float(input) * 2) NO! YES! CompSci 101 - Principles of Programming5

6. Doing Calculations  The following mathematical operators can be used with integers and with floating point numbers:  Addition +  Subtraction-  Multiplication*  Division/ and //  Exponentiation**  Modulus % result1 = 25 / 4 + 4 * (10 % 3) result2 = 25 - 7 * (3 + 12) / 3 result3 = 17 % 5 ** 2 - 12 + 15 result4 = 4 ** 2 // 5 / 2 print(result1, result2, result3, result4) result1 = 25 / 4 + 4 * (10 % 3) result2 = 25 - 7 * (3 + 12) / 3 result3 = 17 % 5 ** 2 - 12 + 15 result4 = 4 ** 2 // 5 / 2 print(result1, result2, result3, result4) B - Brackets Exponents (**) Multiplication, Division, Modulus, Integer division Addition, Subtraction B - Brackets Exponents (**) Multiplication, Division, Modulus, Integer division Addition, Subtraction CompSci 101 - Principles of Programming6

7. Assignment operator  Variables can only store one value. Any value assigned to a variable replaces the value previously stored in the variable. a = 3 b = 12 c = 6 d = 1 d = d * a c = c + 2 * a d = d - b // c c = c * b % c b = b // 2 print (a, b, c, d) a = 3 b = 12 c = 6 d = 1 d = d * a c = c + 2 * a d = d - b // c c = c * b % c b = b // 2 print (a, b, c, d) CompSci 101 - Principles of Programming7

8. math module  The math module contains lots of useful functions: import math def main(): area = 221.67 radius = math.sqrt(area / math.pi) print("Radius of circle", radius) main() import math def main(): area = 221.67 radius = math.sqrt(area / math.pi) print("Radius of circle", radius) main() CompSci 101 - Principles of Programming8

9. Manipulating string objects  strings: the len() function, string slicing, string indices, repeating a string words = "Cheeky one" letter1 = words[0] position = len(words) - 2 letter2 = words[position] print(letter1, letter2) first_part = words[0:4] second_part = words[5:8] print(second_part, first_part) first_part = words[:3] second_part = words[7:] print(second_part, first_part) encouragement = "Go! " encouragement = encouragement * 4 print(encouragement) words = "Cheeky one" letter1 = words[0] position = len(words) - 2 letter2 = words[position] print(letter1, letter2) first_part = words[0:4] second_part = words[5:8] print(second_part, first_part) first_part = words[:3] second_part = words[7:] print(second_part, first_part) encouragement = "Go! " encouragement = encouragement * 4 print(encouragement) CompSci 101 - Principles of Programming9

10. Dot notation with string objects  String instances have many methods which can be applied to them such as upper(), lower(), find(), strip(), rfind() words = "Bim Bam" words_lower = words.lower() words_upper = words.upper() print(words, words_lower, words_upper) words = "Sweety pie" postion1 = words.find("e") postion2 = words.rfind("e") postion3 = words.rfind("ty") position4 = words.rfind("typ") print(postion1, postion2, postion3, position4) letters1 = " Sugar pie " letters2 = letters1.strip() print(len(letters2)) words = "Bim Bam" words_lower = words.lower() words_upper = words.upper() print(words, words_lower, words_upper) words = "Sweety pie" postion1 = words.find("e") postion2 = words.rfind("e") postion3 = words.rfind("ty") position4 = words.rfind("typ") print(postion1, postion2, postion3, position4) letters1 = " Sugar pie " letters2 = letters1.strip() print(len(letters2)) CompSci 101 - Principles of Programming10

11. Common Python inbuilt functions  Inbuilt: len(), min(), max(), round(), abs() number = min(32.7, max(16.4, 3, -1.1), min(56.99, 32.2)) print(number) num1 = 32.657123 num2 = -16.48926 print(round(num1)) print(round(num2)) print(round(num1, 2)) print(round(num2, 3)) num1 = 10 num2 = 20 num3 = abs(num1 – num2) print(num3) number = min(32.7, max(16.4, 3, -1.1), min(56.99, 32.2)) print(number) num1 = 32.657123 num2 = -16.48926 print(round(num1)) print(round(num2)) print(round(num1, 2)) print(round(num2, 3)) num1 = 10 num2 = 20 num3 = abs(num1 – num2) print(num3) CompSci 101 - Principles of Programming11

12. Getting input from the user  The input() function is used to get input from the user. The input() function returns a string. age = input("Enter age: ") print(age * 2, age * 3, age * 4) number = input("Enter number: ") number = int(number) print(number * 2, number * 3, number * 4) age = input("Enter age: ") print(age * 2, age * 3, age * 4) number = input("Enter number: ") number = int(number) print(number * 2, number * 3, number * 4) Enter age: 5 Enter number: 5 Enter age: 5 Enter number: 5 CompSci 101 - Principles of Programming12

13. Random numbers  What is the biggest value which can be printed?  What is the smallest value which can be printed? import random def main(): num1 = random.randrange(2, 15, 3) num2 = random.randrange(24, 27, 2) num3 = num1 + num2 print(num3) main() import random def main(): num1 = random.randrange(2, 15, 3) num2 = random.randrange(24, 27, 2) num3 = num1 + num2 print(num3) main() CompSci 101 - Principles of Programming13

14. Syntax of a Python function  Format of a function def function_name(comma_separated_parameters): statements in the function return value_to_be_returned def function_name(comma_separated_parameters): statements in the function return value_to_be_returned Function nameFunction parameters colon 'def' Indentation (either 1 tab or 4 spaces) Return value'return' Statements in the body of the function. CompSci 101 - Principles of Programming14

15. Python functions def display_welcome(name): message = "Welcome **" + name + " **" print(message) def main(): display_welcome("Sam") def display_welcome(name): message = "Welcome **" + name + " **" print(message) def main(): display_welcome("Sam") def display_welcome(name): message = "Welcome **" + name + " **" print(message) return def main(): display_welcome("Sam") def display_welcome(name): message = "Welcome **" + name + " **" print(message) return def main(): display_welcome("Sam") Both functions do the same thing. The return is optional. CompSci 101 - Principles of Programming15

16. Defining functions  Complete the definition of the check_sum() function, which returns True if the sum of the first three parameter values is equal to the fourth parameter value, otherwise the method returns False. def check_sum( ): def main(): print(check_sum(15, 2, 7, 24)) print(check_sum(10, 2, 3, 24)) main() def check_sum( ): def main(): print(check_sum(15, 2, 7, 24)) print(check_sum(10, 2, 3, 24)) main() True False True False CompSci 101 - Principles of Programming16

17. Defining functions  Complete the definition of the get_next_even() function which returns the first even number greater than the parameter number. def get_next_even( ): def main(): print(get_next_even(15)) print(get_next_even(10)) main() def get_next_even( ): def main(): print(get_next_even(15)) print(get_next_even(10)) main() 16 12 16 12 CompSci 101 - Principles of Programming17

18. Code trace Show the code trace and the output for the program def main(): years = 5 result = test1(years) print("A", result) result = test2(years + 5) print("B", years) def test1(num): print("C", num) num = test2(num) + 4 return num def test2(num1): num1 = max(num1 + 1, 10) print("D", num1) return num1 main() def main(): years = 5 result = test1(years) print("A", result) result = test2(years + 5) print("B", years) def test1(num): print("C", num) num = test2(num) + 4 return num def test2(num1): num1 = max(num1 + 1, 10) print("D", num1) return num1 main() years 5 main() function CompSci 101 - Principles of Programming18

19.  Booleans represent "truth" values, i.e., True or False  Relational operators compare two different things, which evaluates to Boolean values  Boolean Operators are: and, or and not, e.g., (age=24, gender='F')  (age > 18) and (gender == 'F') is True  (age > 34) or (gender == 'M') is False  not (age > 18) is False Boolean expression 19COMPSCI 101 - Principles of Programming DescriptionOperatorExample Equals==age == 10 Less than<age < 10 Less than or equal<=age <= 10 Greater than>age > 10 Greater than or equal>=age >= 10

20. If statements x = 10 y = 5 if x < 10: if y != 5: print("A") else: print("B") elif y > 10: print("C") else: if y != 5: print("D") else: print("E") x = 10 y = 5 if x < 10: if y != 5: print("A") else: print("B") elif y > 10: print("C") else: if y != 5: print("D") else: print("E") a = 4 b = 12 c = 37 d = 51 if a < b: print("A") if a > b: print("B") if d <= c: print("C") if c != d: print("D") a = 4 b = 12 c = 37 d = 51 if a < b: print("A") if a > b: print("B") if d <= c: print("C") if c != d: print("D") CompSci 101 - Principles of Programming20 Give the output

21. Repetition – while loops  Give the possible output: import random def main(): sum = 0 while sum < 10: number = random.randrange(1, 7) sum += number print(sum, number) final_sum = sum – number print("Finally", final_sum) main() import random def main(): sum = 0 while sum < 10: number = random.randrange(1, 7) sum += number print(sum, number) final_sum = sum – number print("Finally", final_sum) main() while boolean_expression: indented_code_block CompSci 101 - Principles of Programming21

22. range(start, stop, step) function  The range() function defines a sequence of values within the boundaries (exludes the last value). The step parameter is optional. A for...in loop can be used to repeat code for each element in the specified range. Give the output. number = 50 for num in range(10, 1, -4): number = number – num print("number:", number) sum = 0 for number in range(10, 16, 2): sum += number print("sum:", sum) number = 50 for num in range(10, 1, -4): number = number – num print("number:", number) sum = 0 for number in range(10, 16, 2): sum += number print("sum:", sum) number: sum: number: sum: CompSci 101 - Principles of Programming22

23. Repetition – for loops  Give the possible output: def count_vowels(words): vowels = "aeiouAEIOU" length = len(words) count = 0 for i in range(length): if vowels.find(words[i]) != -1: count = count + 1 return count def main(): word = input("Enter the word(s): ") print("Output: " + str(count_vowels(word)) + ".") main() def count_vowels(words): vowels = "aeiouAEIOU" length = len(words) count = 0 for i in range(length): if vowels.find(words[i]) != -1: count = count + 1 return count def main(): word = input("Enter the word(s): ") print("Output: " + str(count_vowels(word)) + ".") main() for var_name in range(start, stop, step): indented_code_block CompSci 101 - Principles of Programming23

24. Lists  A list is a sequence of comma separated elements within square brackets.  Elements of a list can be accessed using the index.  The '+' operator can be used to add a new element to the end of a list my_list = [1, 2, 3] my_list[1] = my_list[0] + my_list[2] my_list[0] = my_list[1] + my_list[2] my_list[2] = my_list[0] + my_list[1] print(my_list) my_list = [1, 2, 3] my_list[1] = my_list[0] + my_list[2] my_list[0] = my_list[1] + my_list[2] my_list[2] = my_list[0] + my_list[1] print(my_list) CompSci 101 - Principles of Programming24 Give the output

25. Lists  A list is a sequence of comma separated elements within square brackets.  The elements of a list can be traversed using a for…in loop.  The elements of a list can be changed using the index value. my_list = [2, 6, 3] b = 0 print("NOT changing list elements") for element in my_list: element = element + 2 b += element print("b:", b) print("my_list:", my_list) print("Changing list elements") for index in range(len(my_list)): my_list[index] = my_list[index] + index print("my_list:", my_list) my_list = [2, 6, 3] b = 0 print("NOT changing list elements") for element in my_list: element = element + 2 b += element print("b:", b) print("my_list:", my_list) print("Changing list elements") for index in range(len(my_list)): my_list[index] = my_list[index] + index print("my_list:", my_list) NOT changing list elements b:17 my_list:[2,6,3] Changing list elements my_list:[2,7,5] NOT changing list elements b:17 my_list:[2,6,3] Changing list elements my_list:[2,7,5] CompSci 101 - Principles of Programming25 Give the output

26. Sequences and for loops  A string is a sequence. Each element of the string sequence (i.e., each character) can be accessed using a for loop: phrase = "Give it a go" count = 0 for letter in phrase: if letter in "aeiouAEIOU": count += 1 print("count", count) phrase = "Give it a go" count = 0 for letter in phrase: if letter in "aeiouAEIOU": count += 1 print("count", count) for item in sequence: indented_code_block CompSci 101 - Principles of Programming26

27. Split a string into a list of words  The split() method splits a string into its parts. Default split (the delimiter) is white space (e.g., words.split())  Can use any other delimiters (e.g., words.split(", "), lines.split("\n")) lots_of_words = "Whether you think you can or you think you can't, you are right" my_list = lots_of_words.split() count = 0 for word in my_list: if len(word) == 3: count += 1 print("count: ", count) lots_of_words = "Whether you think you can or you think you can't, you are right" my_list = lots_of_words.split() count = 0 for word in my_list: if len(word) == 3: count += 1 print("count: ", count) Count: 7 CompSci 101 - Principles of Programming27

28.  The test is worth 15% of your final mark, which covers the topics up to Lecture 15 (included).  Date and Time: Tuesday 5th May 6:30pm - 7:45pm.  Please bring your Student Id card, a pencil and an eraser.  The test is a closed book test, so you cannot refer to any material during the test. Calculators are not permitted.  Please arrive by 6:15pm as you will be given 5 minutes' reading time.  The first part of the test is Multi-Choice Questions (2/3) and the second part of test is written questions (1/3).  Please notify Angela Chang if you have a test clash. Test Next Week - Tuesday (5th May) 28CompSci 101 - Principles of Programming