Count Controlled LoopsLook at the little children …Why is the sun’s face features orange …

Warm Up Practice Write a program that continually asks the user for a

price value

When the user enters the word “end” you should end the program and add the total price of all the products

In addition, display the highest priced item and the lowest priced item

Count Controlled Loops Previously, we learned the “while” loop, which we

defined as the condition controlled loop

It is so called “condition controlled” because it iterates the number of times in which a Boolean expression holds True

Today, we will look at what is called a “count controlled” loop

Count Controlled Loops It is called “count controlled” because it iterates a

specific number of times

It is not dependent on the truth value of a Boolean expression, or condition

Count Controlled Loop Now, it’s important to remember that a lot of times

in Python, we can accomplish the same tasks with various different methods i.e. ELIF’s versus nested IF’s

In the same way, a count controlled loop can be created by using a “while” loop

These various methods are really for convenience’s sake

(We should also note that a while loop can be duplicated by a function controlled loop)

Count Controlled LoopExample:

counter = 0

while counter < 5:

print (“this will print 5 times!”)

counter +=1

Lists Python has such things called “lists”

Lists are denoted by brackets [ a, b, c, d ] and each item in the list is separated by commas

Lists can be stored and named as variables

Example:

x = [a, b, c, d]

Lists One important thing to note about lists is that they

can hold various data types all at once

Example:

list = [“name”, “word”, 1, 2, 3]

The ‘’for’’ loop The “for” loop is Python’s native count controlled

loop

Example:

for num in [1, 2, 3, 4, 5]:

print(“this will also print 5 times”)

The ‘’for’’ loop The “for” keyword starts the loop

The “num” is the name of the target variable

“in” is another keyword

[1, 2, 3, 4, 5] is the list of items to iterate over

Note the indentation

The ‘’for’’ loop The “for” loop will iterate once for each item in the

list passed to it when the loop begins

During the first iteration, the target variable will assume the value of the first item in the list

During the second iteration, it will assume the second item in the list

This continues until you reach the end of the list

The ‘’for’’ loop

for x in [1, 2, 3, 4, 5]: >> 1

print (x) 2

3

4

5

The ‘’for’’ loop

for name in [“Josh”, “Jeen”, “Nicole”]:

print(“My favorite student is”, name)

>> My favorite student is Josh

My favorite student is Jeen

My favorite student is Nicole

Practice – Make Dat DOE Write a program that asks the user how much

money they made from Monday to Sunday

The program should specify the day each time it asks the user for a value

Then sum up the total amount they made and print out

Practice – Mechanics Rewrite the following loop as a “while” loop:

for x in [10, 20, 30, 40]:

print (x)

The range( ) Function So far, we’ve been TIRELESSLY writing out lists of

pre-defined values in our “for” loops

The range( ) function allows us to dynamically generate lists based on pre-determined criteria

The range( ) Function

for x in range(5): >> iteration # 0

print(“iteration #”, x) iteration # 1

iteration # 2

iteration # 3

iteration # 4

The range( ) Function The range( ) function takes at least one argument

In it’s simplest form, it takes a single integer

The range( ) function returns what we can think of as a list in Python

When passed a single integer, it will return a list of integers from 0 to the number specific minus one

The range( ) Function

range(5) [ 0, 1, 2, 3, 4]

range (10) [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

The range( ) Function However, the range( ) function can behave in

different ways

It can take two arguments, which sets a start and an end value

By default, the function increments by 1

range (1, 5) [ 1, 2, 3, 4]

range (5, 10) [ 5, 6, 7, 8, 9]

The range( ) Function You can also pass three arguments and set a start

value, an end value, and a step value

range(0, 10, 2) [0, 2, 4, 6, 8]

range(1, 15, 3) [1, 4, 7, 10, 13]

If the step count does not perfectly fall on the end value, it will just include the number before the end value is reached

The range( ) Function Lastly, you can ask the range( ) function to count backwards by passing in a negative step count

Practice – Countdown Write a program that counts down from 10 and then print out “HAPPY NEW YEAR!”

Import ‘’time’’ We’ll talk more about this later, but another module

we can import into Python is “time”

We can ask Python to pause (for dramatic effect) by calling the sleep( ) function in time

The sleep( ) function can take one argument, denoting the number of seconds to “sleep”

**sleep( ) can also take floats

Import ‘’time’’ import time

for x in range(10, 0, -1):

print(x)

time.sleep(1)

print(“HAPPY NEW YEAR!”)

Loop Targets In a “for” loop, we generally use the target variable

as a reference value for some kind of calculation

Remember that the value of the target variable changes with each iteration of the loop

Practice – Squares Write a program that calculates the square of the

numbers between 1 and 10

Print out the number and it’s square as your loop iterates

Practice – Stair Master Write a program that prints out the following:

** (2 stars)

**** (4 stars)

****** (6 stars)

******** (8 stars)

********** (10 stars)

************ (12 stars)

Practice – Divisibility Write a program that asks the user for an integer

Then print out all numbers that are divisible by that number from 1 to 1,000

Practice – Divisibility (extension) Extend your divisibility program to check for all

integers from 1 to 10,000 that are divisible by two different integers simultaneously

Print out 10 numbers per line

User Controlled Ranges Sometimes, we need to ask the user to control the

# of iterations within a loop

You can do this by substituting a variable within the range( ) function to control the start, end, and step values of the list that will be generated

User Controlled Ranges x = int(input(“start value: “))

y = int(input(“end value: “))

z = int(input(“step value: “))

range(x, y, z)

User Controlled Ranges We can also just put the input( ) function directly

into the range( ) function

However, we must remember to convert it into an integer

User Controlled Ranges

range(int(input(“start: “)), int(input(“end: “)), int(input(“step: “))) Just be careful, as this can be confusing and you

need to keep count of how many parentheses you use