Discussion - Friday, 2/18/2011

Topics: Format strings, escape sequences, loops

Complete the exercises at the end of this document!

Formatting Strings:

Controlling the appearance of output in print statements

Controlling the appearance of output in print statements

Format strings for different types:

%f -- used for floating point numbers

%e and %E -- used for floating point numbers in exponential form

%d -- used for integers

%s -- used for strings

Example with floating point numbers:

print "%.2f and %.4f are my favorite numbers!" % (3.14159, 2.71835)

Output:

3.14 and 2.7184 are my favorite numbers!

Note: For the two values in the above example, we are printing:

- 2 digits after the decimal point for the first number (%.2f), and
- 4 digits (%.4f) after the decimal point in the second number.

Example with integers and strings:

print '%s is %d years old' % ('Elvis', 25)

Output:

Elvis is 25 years old

Loop Review

while loops:

while <some condition>:

statement

statement

...

statement

Example:

number = 10

while number >= 7:

print number

number = number - 1

What is the output??

for loops

for i in sequence:

statement

...

statement

Note: Execute the body of the loop once for each value of i in the sequence.

Example:

for i in [1, 2, 3]:

print i

What is the output?

Example:

sum = 0

for i in range(1, 5):

sum = sum + i

print 'The sum is %d.' % sum

Output?

Escape Sequences

Use escape sequences inside quotes in print statements: these 2 character sequences start with a backslash.

\t -- tab

\n -- carriage return

\\ -- display a backslash

Example:

print 'Hello\n\tworld'

Output:

Hello

world

Exercises:

1. Write a program that uses a for loop to compute the sum of the even integers from 12 to 100.

2. Read two numbers from the user, and print their sum. Note that you must use a format string to produce the output.

Sample Run:

First number? 10

Second number? 12

The sum is 22.

3. Use a while loop to print 99, 96, 93, ..., 3 in this order to the screen, one number per line.

4. Write a function make10 that, given two ints a and b, prints True if one of them is 10 or if their sum is 10.

def make10(a, b):

# finish the function definition