Transcript Python_(Control_Structures_WHILE_loops)

Control Structures
WHILE Statement
Looping
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REPITITION
…or Iteration
…a step or sequence of steps
that are repeated until some
condition is satisfied.
Sometimes we want to repeat a bit of code many times. We use loops
to achieve this!
For example, if you wanted to output the same statement 3 times, we
would use a FOR loop. This is because we know the number of
iterations.
RULE: use a FOR loop if the number of iterations is known.
What if we don’t know the number of iterations?
For example, iterate until the user enters a specific value…
WHILE Loop
If condition is true
Condition ?
If condition is false
Execute code block
Like if statements, while loops
evaluate whether a condition is true
or false!
The block is evaluated (iterated)
until the condition becomes false.
Looping mechanisms in python…
In Python, there are 2 looping mechanisms…
WHILE
LOOP
FOR
LOOP
LOOPS for a an unknown number of
times!
For example, output HELLO WORLD
? times until user types quit.
LOOPS for a specified
number of times!
For example, output HELLO WORLD 3 times
Syntax
while <condition>:
<block of code executed>
Example, prompt the user to guess the password (dalriada)
>>>password = (‘dalriada‘)
guess = input(‘Please enter password: ‘)
while guess != password:
print(‘Access denied')
guess = input(‘Please try again’)
print(‘Access granted’)
What will be output here?
What will be output here?
>>>number =1
while number < 5:
print(number*number)
number = number + 1
What will be output here?
>>>while x < 5:
print(‘Hello’)