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Introduction to Programming: Understanding Booleans, Branching, and Loops in Python

This introductory programming course covers essential Python concepts, including Boolean values, comparison operators, and control flow through branching with IF-ELSE statements and loop constructs such as WHILE. Students will learn about keyword significance in Python, the importance of indentation, and how to manage program flow using ‘break’ and ‘continue’. The session includes a demonstration of the "Guess My Number" game and practical lab work on simulating a coin flip. No previous experience is required, making it perfect for beginners.

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Introduction to Programming: Understanding Booleans, Branching, and Loops in Python

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Presentation Transcript

  1. Course A201:Introduction to Programming 09/16/2010

  2. Outlines for today • A new type of value: Boolean • Concept of keyword and indentation • Several basic concepts about Branching • IF - ELSE – IF and WHILE loop • Keep trace: what’s the stop condition • How and when to use “break” and “continue” • Demonstration of “Guess My Number Game”

  3. Boolean and Comparison Operators • Boolean values: True or False • Statements that will generate boolean values: 1 == 1 True 2 <= 0 False 4 > 1 True 9 != 99 True “1” == 1 False • These are Comparison operators

  4. keyword • In Assignment 1, question 2, the last variable is “for”, which seams legit but actually not This is a KEYWORD • Keywords are a set of words that have special/predefined meanings: for, if, else, while, break, import, from They will appear in orange in .py files in IDLE.

  5. Indentation • In Python, proper indentations are crucial -> • Python use indentations to determine the structure of if-else blocks, while blocks, etc. • If you forget to have indentations, it will give you syntax error • Enter tab if user == “bye”: print ( “bye!” ) elif user == “hi”: print( “Hi” ) else: print(“…”)

  6. Conditional: IF if user == “bye”: print ( “bye!” ) elif user == “hi”: print( “Hi” ) else: print(“…”) • Don’t forget the COLON • You can have only IF, or IF-ELSE, or IF-ELIF, or IF-ELIF-ELSE • You can have another IF block inside a IF block: • if …: • if …: • some statements

  7. Conditional: WHILE gpa = 0.0 while gpa <= 4.0: gpa = float(raw_input(“Enter GPA: ” )) print(“Not high enough” ) • While [this condition] is true, keep executing the [statements in here] • Creating loops, make repetitive tasks easier

  8. Keep trace • What’s wrong with this program: health = 10 trolls = 0 damage = 3 while health != 0: trolls += 1 health -= damage

  9. Keep trace Health trolls damage health!= 0 10 0 3 True 7 1 3 True 4 2 3 True 1 3 3 True -2 4 3 True -5 5 3 True -7 6 3 True

  10. Keep trace • What’s wrong with this program: health = 10 trolls = 0 damage = 3 while health != 0: trolls += 1 health -= damage • <- This condition will be true FOREVER!!!

  11. Keep trace • What’s wrong with this program: health = 10 trolls = 0 damage = 3 while health > 0: trolls += 1 health -= damage • <- You have to confirm that this condition will be false at some time

  12. Usage of break gpa = 0.0 while True: gpa = float(raw_input(“Enter GPA: ” )) if gpa > 4.0: break • Break out of the loop

  13. Usage of continue counter = 0 while counter <= 10: count += counter if count == 5 continue print(counter) print(“-” * 20) • The output won’t include 5. • When you reach continue, the rest of code (in the red rectangle) will be omitted, computer goes straight to next interation.

  14. Guess My Number Game • pick a random number • while the player hasn't guessed the number, let the player guess • If guess is right, congratulate the player

  15. Lab work • Write a program that flips a coin 100 times and then tells you the number of head and tails • Modify your program so that it prompts the user for the number of times to flip the coin • On paper in English first, on computer in Python next • Optional team work

  16. Have a nice evening! • See you tomorrow~

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