Introduction to Programming 09162010 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 ID: 616027
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Slide1
Course A201:Introduction to Programming
09/16/2010Slide2
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”Slide3
Boolean and Comparison Operators
Boolean values:
True
or
False
Statements that will generate boolean values:1 == 1 True2 <= 0 False4 > 1 True9 != 99 True“1” == 1 False
These are Comparison
operatorsSlide4
keyword
In Assignment 1, question 2, the last variable is “
for
”, which seams legit but actually not
This is a
KEYWORDKeywords 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.Slide5
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(
“…”
)
Slide6
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 statementsSlide7
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 easierSlide8
Keep trace
What’s wrong with this program:
health = 10
trolls = 0
damage = 3
while health != 0: trolls += 1 health -= damageSlide9
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 TrueSlide10
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!!!Slide11
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 timeSlide12
Usage of break
gpa
= 0.0
while
True: gpa = float(raw_input(“Enter GPA: ” )) if gpa > 4.0: breakBreak out of the loopSlide13
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
nex
t
interation
.Slide14
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 playerSlide15
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 workSlide16
Have a nice evening
!
See you tomorrow~