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# Line Continuation, Output Formatting, and Decision Structures - PowerPoint PPT Presentation

Line Continuation, Output Formatting, and Decision Structures. CS303E: Elements of Computers and Programming. Line Continuation. What do you do if your line of Python code is too long? Use the line continuation character! the backslash character \ Place at the very end of the line

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### Line Continuation, Output Formatting, and Decision Structures

CS303E: Elements of Computers and Programming

Line Continuation Structures

• What do you do if your line of Python code is too long?

• Use the line continuation character!

• the backslash character \

• Place at the very end of the line

• Python interpreter will assume the next line is part of the same line

Line Continuation: Example Structures

>>> sum = 2.35 + 8 \

+ 13.6 + \

25

>>> sum

48.950000000000003

>>> print “\t\nHello, my name is”, \

“Jarvis”

Hello, my name is Jarvis

Output Formatting Structures

• We’ve seen this:

print “The temperature is”,temp,”degrees”

• Now, we’ll see another way

• Better able to control how print displays values

• 88.33333333 -> 88.33

• 4 / 15 / 2010 -> 4/15/2010

Output Formatting: StructuresFormat Operators

print “The temperature is %d degrees” % temp

• String formatting operator: %

• NOT modulus: modulus operates on numbers

• Appears in strings

• Indicates how and where a value should be printed in a string

• Also indicates end of print string and beginning of the values to be printed

Output Formatting: StructuresFormat Operators

print “The temperature is %d degrees” % temp

Indicates the type and format of the value

Indicates the end of the string to be printed and the beginning of the values specified in the string

Output Formatting: StructuresFormat Specifiers

• For each, you can also specify width and precision:

%<width>.<precision><type character>

print “The average is %3.2f” % avg

Output Formatting: StructuresEmbedded Operations

You can calculate values in your print statement:

print “2+3 = %d” % (2+3)

print “x/y = %.2f” % (x/y)

Formatting Example Structures

>>> import math # package containing pi

>>> math.pi #display the value of pi

3.1415926535897931

>>> #Now display with 4 digits after decimal point

>>> print “Pi: %.4f” % math.pi

Pi: 3.1416

Notes:

• The f in the format string stands for float.

• The number appears in the output wherever the format string occurs.

• The number is rounded to the specified number of digits.

Formatting Example Structures

• Can specify a minimum field width for the display of a value

• Minimum width comes before the decimal point in the format string

• >>> print “Pi: %7.3f” % math.pi

• Pi = 3.142

• The field width is 7:

• digits and decimal point: width 5

• 2 blank spaces to left of number

Formatting: Two or More Values Structures

• Enclose multiple values in parentheses

• Separate the values with commas

print “First name: %10s, Last Name: %12s” % (“Elvis”, “Presley”)

First name: Elvis, Last Name: Presley

Output Formatting: StructuresExamples

• Modify average.py to print 2 decimal places of the average

• Practice printing strings from raw_input()

• Print using multiple values

• The values must be enclosed in parentheses

Question for you: StructuresOutput Formatting

What is the expected output?

x = 5.7

y = 2.18

print “x+y=%.1f” % (x+y)

A. 7 C. 7.9

B. 7.8 D. 8

Comparisons Structures

• Allows you to compare two values

• Result in a True or False value

• type Boolean (bool)

• You can compare numbers or strings, literals, variables, or expressions

How do you specify a comparison? Structures

• Specify the condition using a relational operator

Comparisons: StructuresExamples

• test = 13 < 15

• test = 101 >= 99

• test = “a” < “b”

• test = 4 == 2+2

• test = 15 != 16

• test = 12 == 3*5

Lexicographic Order Structures

• Strings are rated according to lexicographic order

• Orders words A-Za-z

• Capital letters first in alphabetical order

• Lower-case letters second in alphabetical order

• NOT in dictionary order

Decisions Structures“Once you make a decision, the universe conspires to make it happen.”-- Ralph Waldo Emerson

• Gives you the ability to specify different instructions based on a condition

• The condition is typically a comparison

if some comparison is true:

do something

Decisions: Structuresif Statement

def main():

command

if(<condition>):

command

command

command

command

main()

Commands not dependent on the condition

Commands only executed if condition is true

Commands not dependent on the condition

Indentation matters! (Again)

if Structures examples

number = 25

if number > 10:

print number, “is greater than 10!”

Output:

25 is greater than 10!

Decisions: Structuresif-else Statement

if(<condition>):

command

command

else:

command

command

Commands only executed if condition is True

Commands only executed if condition is False

if-else Structuresexercise

• Write a program that asks the user to enter a number. If the number is 3, print a message indicating that they entered your favorite number, and otherwise, indicate that you don’t like the chosen number.

Decisions: Structuresif-elif-else Statement

if(<condition>):

command

command

elif(<condition>):

command

command

else:

command

command

Commands only executed if condition is True

Commands only executed if earlier conditions are False and this condition is True

You can used as many of these as you like

Commands only executed if EVERY condition is False

if- Structureselif-else example

if number < 10:

print number, “is small”

elif number < 100:

print number, “is pretty big”

elif number < 500:

print number, “is big”

else:

print “Wow, a really big number!”

Sample Run:

355 is big

Decisions: StructuresNested ifs

You can put if statements inside the body of the if (or elif or else) statement:

if(<condition>):

if(<some other condition>):

command

else:

command

elif(<condition>):

Decisions: StructuresGotchas

• Exactly ONE of the bodies in if-elif-else will be executed

• Only the first True condition

• Comparison of floats

if(.3 == .1+.2) is False

Question for you: StructuresDecisions

What is the expected output?

if(125<140):

print “first one”

elif(156>=140):

print “second one”

else:

print “third one”

A. first one C. third one

B. second one D. first one

second one