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Mastery Objective:. Students will understand how to use while loops in computer programming. Agenda.

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### Mastery Objective:

Students will understand how to use while loops in computer programming

Agenda
• If-else and if-elif-else assignment due tomorrow (Wednesday) by the end of class with no scheduled in class time. If you haven’t finished the assignment, plan to stay after or come in early to finish the assignment.
• Notes: While loops
• Programming assignments
While loops

Basic principle:

• While something is true, repeat something

Basic structure:

while response != “Because.”:

response = raw_input(“Why? “)

Similarities and differences between if and while structure
• In both structures, if the condition is true, the block is executed.
• What is different: In the while structure, the block is executed until it is false.
Sentry Variable
• Often, sentry variables control the while loop
• response variable in example code

while response != “Because.”:

response = raw_input(“Why? “)

• Must be intialized prior to use, usually right before while loop. Usually initialized to empty variable

response = “ “

example

response = “”

while response !=“No”:

response = “raw_input(“Try again!”):

print “All done!”

Infinite Loop
• Loop that never ends.
• Example

counter = 0

while counter <=10

print counter

Forgot to increase counter variable

Counter +=1

Setting values as true or false

When using numbers: 0 is false other numbers are true

if money:

print “Thank you!”

else:

print “I am sorry there are no seats available.”

Intentional Infinity loops
• There is a place for infinite loops

Count = 0

While Ture:

count +=1

if count >10:

break (breaks loop)

if count ==5;

print count

Break and Continue
• Used in any type of loop
• Should be used sparingly
Using compound conditions
• Uses logical operators
not Logical Operator Example