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Course A201: Introduction to Programming

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

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Course A201: Introduction to Programming

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  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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