Chapter 10 While Loop

1
Chapter 10 While Loop

• Bernard Chen 2007

2
Loop

• In this chapter, we see two main looping
  constructs --- statements that repeat an action
  over and over
• The for statement, is designed for stepping
  through the items in a sequence object and
  running a block of code for each item
• The while loop, provides a way to code general
  loop

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While Loop

• It repeatedly executes a block of indented
  statements, as long as a test at the top keeps
  evaluating to a true statement.
• The body never runs if the test is false to begin
  with

4
While Loop General Format

• The while statement consists of a header line
  with a test expression, a body of one or more
  indented statement
• while lttestgt
• ltstatementgt

5
While Loop Examples

• Print from 0 to 10
• gtgtgt count0
• gtgtgt while countlt10
• print count
• countcount1

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While Loop Examples

• This example keeps slicing off the first
  character of a string, until the string is empty
  and hence false
• gtgtgt xPython
• gtgtgt while x
• print x
• xx1

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While Loop Examples

• Infinite loop example (always keep the test true)
• gtgtgt while 1
• print Type Ctrl-C to stop me!!

8
While Loop Examples

• So how to print
• by using while loop?

9
While Loop Examples

• gtgtgt num6
• gtgtgt while numgt0
• print num
• num num-1

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While Loop Examples

• Then, how to print
• by using while loop?

11
While Loop Examples

• gtgtgt num0
• gtgtgt while numlt6
• print num
• num num1

12
While Loop Examples

• How to simulate range function in for loop?
• gtgtgtfor i in range(0,10,2)
• print i
• gtgtgti0
• gtgtgtwhile ilt10
• print i
• ii2