9/1/2013
Announcements
15-112 Fundamentals of
Programming
Read pages 29 – 38 (Do not read the
section on Break, Continue, and Pass)
Reading Quiz due next class
Assignment 1 is due Tuesday
Sept 1st 2013
What are we doing today?
Calling functions
Writing functions
Functions with parameters
Functions with return values
Let’s first finish up last lecture
Indexing and Slicing
 Used to manipulate information in a string
name = "Chris Myers"
print name[2:4]
print name[:4]
print name [3:]
print name[:]
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We have used functions before
What does ord function do?
What does chr function do?
What does math.sin function do?
Functions that do something
Some functions just perform a task
def doSomething():
print(“CMU Rocks!”)
How would you use this function
doSomething()
doSomething()
Functions
Function is a way of packaging a group of
instructions that perform a specific task
Functions abstract out the “what” from the
“how”
 When we use a function, we worry about
“What” needs to be done and NOT “how” it
will be done
 When we write a function we worry about the
“how”.
Functions that act on input
Some functions perform a tasks on values
that you give them
 printSquare – A function that takes a number
and prints its square
 How will you use this function?
printSquare(2)
printSquare(3)
 How will you define this function?
def printSquare(x):
print x, "**2 =", (x*x)
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Function definition
def SomeName (Input parameters if any):
Function Body
Function Body
Function Body
Using Functions
A function has to be defined before it can
be used!
A complete example – funtest.py
def printSquare(x):
print x, "**2 =", (x*x)
printSquare(2)
printSquare(3)
Functions - multiple parameters
Functions with return values
Functions can take several parameters
Functions can return values
def printSum(x,y):
print x, "+", y, "=", x+y
def square(x):
return x*x
printSum(2,3)
printSum(3,4)
print square(3)
print square(4)
a = square(3) + square(4)
print a
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Exercise
What we know so far
Ask the user for their name, and then print the
user’s initials.
Create a function called getEggCartons:
 This function should take as input parameter
number of egg and return the number of cartons
required to hold that many eggs (given that each
egg carton holds one dozen eggs, and you cannot
buy fractional egg cartons).
Read the number of eggs from the user and
use the above function to calculate the number
of Cartons user should buy
Sequential Execution
Conditional Execution
All execution of instructions so far has
been sequential
Step 1
Example:
print "Hello to my sequential program“
How to get input from the user
How to print messages
Three type of values
Basic Arithmetic
Expressions
Variables
Functions
Step 2
name = raw_input("Enter your name> ")
Sometimes we want to selectively
execute statement
 If your name is same as mine, I should say
something.
name = raw_input("Enter your name> ")
print "Oh Wow! Your name is same as mine"
Step 3
age = int(raw_input("Enter your age> "))
Step 4
 Is there anything wrong with this?
print name,", you are ", age , "years old"
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Conditional Execution
We can fix this by using conditional
execution
name = raw_input("Enter your name> ")
Colon
if name == "saquib" :
print "Oh Wow! Your name is same as mine"
Indented
Conditional Execution
Conditional execution finishes when
you stop indenting
name = raw_input("Enter your name> ")
if (name == "saquib"):
print "Oh Wow! Your name is same as mine"
print "I really like our name"
print "Welcome to my program", name
>>>
Enter your name> saquib
Oh Wow! Your name is same as mine
I really like our name
Welcome to my program saquib
>>>
Conditional Execution
number = int( raw_input("Enter a number "))
if number > 0:
print "The number is positive"
print "Thank you for your number"
>>>
Enter a number 34
The number is positive
Thank you for your number
>>>
>>>
Enter your name> Bob
Welcome to my program Bob
>>>
More on forming conditions
Conditional Operators
 and
 or
 not
>>>
Enter a number -5
Thank you for your number
>>>
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Combining conditions
num1 = int(raw_input())
num2 = int(raw_input())
num3 = int(raw_input())
if num1 > num2 and num1 > num3:
print num1
if num2 > num1 and num2 > num3:
print num2
if num3 > num1 and num3 > num2:
print num3
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