control.md

Control flow: if-else, loops

If-else

If statement example:

x = int(input("Enter a number:"))
if x % 2 == 0:
    print("Odd")
else:
    print("Even")

Anything that evaluates to True or False can be used as an if condition. Examples:

print(3 > 8)
print(3 <= 8)
print(3 % 2 == 0)
print(3 in [1, 2, 3])
print(len([1, 4]) == 1)

Problem: make everything true:

# change the values in this block so that all the numbers 1 to 6 are printed
number = 10
second_number = 10
first_array = []
second_array = [1,2,3]

if number > 15:
    print("1")
if first_array:
    print("2")
if len(second_array) == 2:
    print("3")
if len(first_array) + len(second_array) == 5:
    print("4")
if first_array and first_array[0] == 1:
    print("5")
if not second_number:
    print("6")

Problem: change the value of x in the first line to get this program to print A, then B, then C:

x = 1
if x < 5:
    print('A')
elif x < 10:
    print('B')
else:
    print('C')

What is the difference between the following programs?

x = 1
if x < 5:
    print('A')
elif x > 1:
    print('B')

x = 1
if x < 5:
    print('A')
if x > 1:
    print('B')

x = 1
if x < 5:
    print('A')
    if x > 1:
        print('B')

Loops

Examples of for and while loops, and the break and continue commands:

count = 0
while True:
    print(count)
    count += 1
    if count >= 5:
        break

for x in range(10):
    if x % 2 == 0:
        continue
    print(x)

Problem: write a program that adds up all the numbers from 1 to 100:

# Your code goes here

Problem: loop and print (use both for and while):

import random
numbers = [random.randint(1, 100) for _ in range(100)]
# Your code goes here
# Loop through and print out all even numbers from the numbers list in the same order they are received. Stop printing if you see any number greater than 66.

Here's an example of using a loop to create a list:

new_planet = ''
planets = []
while new_planet.lower() != 'done':
    if new_planet:
        planets.append(new_planet)
    new_planet = input('Enter a new planet, or done if done')
print(planets)

Problem: write a program to play a number guessing game. This is what it should look like:

I'm thinking of a number between 1 and 100.
Enter your guess: 55
My number is greater than 55
Enter your guess: 70
My number is greater than 70
Enter your guess: 66
You guessed it! My number is 66.

Problem: convert a string from CamelCase (MyFunctionName) into the Python format, snake case (my_function_name).

Problem: convert a string from the Python format, snake case (my_function_name), into CamelCase (MyFunctionName).