Conditions and loops

Learning objectives

• Compare values with conditions.
• Use if, elif, and else.
• Repeat work with for and while.
• Avoid infinite loops.

Decisions

battery_percent = 24

if battery_percent < 20:
    message = "Return the robot to its charging station."
elif battery_percent < 50:
    message = "The robot can continue, but monitor the battery."
else:
    message = "The battery level is healthy."

print(message)

The indented block belongs to the condition above it. Comparisons produce True or False.

Repetition

temperatures = [20, 21, 19, 23]

for temperature in temperatures:
    print(f"Recorded temperature: {temperature} C")

Use a while loop when the number of repetitions depends on a condition:

countdown = 3

while countdown > 0:
    print(countdown)
    countdown -= 1

print("Launch!")

The loop must change something that can eventually make its condition false.

Practice

Write a program that examines a list of sensor readings and prints "warning" for readings below 10. Add a counter for the number of warnings.

Checkpoint

Predict how many times each loop runs before executing it. Explain what would happen if countdown -= 1 were removed.

Mini-project

Create a safe robot decision simulator. Given distance readings, print stop when an obstacle is closer than 20 cm and move otherwise. Include at least five readings and report how many stops occurred.