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Chapter 5: Control Flow with Karel

Control flow is one of the most important concepts in programming. It allows Karel to make decisions and repeat actions based on conditions. In this chapter, we'll explore how to use if statements, while loops, and other control structures to make Karel behave intelligently.

While Loops

A while loop allows Karel to repeat a set of commands as long as a certain condition is true. This is incredibly useful when we don't know exactly how many times we need to repeat an action. For example, Karel can move forward until hitting a wall, or pick up beepers until there are none left.

Example: The following code makes Karel move forward until reaching a wall:

while front_is_clear():
    move()

If Statements

The if statement allows Karel to make decisions. Karel can check a condition and execute different code depending on whether the condition is true or false. You can also use else to specify what should happen when the condition is false.

Note: Remember that Karel can check various conditions like front_is_clear(), beepers_present(), facing_north(), and more.

Try It Yourself!

Below is an interactive code editor where you can write Karel programs. Try modifying the code to make Karel perform different tasks. Click Run Code to see your program in action!

Karel Code Editor Write your Karel program below

# Karel Program - Move and Collect Beepers # This program makes Karel move forward and pick up beepers def main(): # Move forward until hitting a wall while front_is_clear(): move() # If there's a beeper, pick it up if beepers_present(): pick_beeper() # Turn around turn_left() turn_left() # Move back to start while front_is_clear(): move() # Available commands: # move() - Move forward one space # turn_left() - Turn 90 degrees left # pick_beeper() - Pick up a beeper # put_beeper() - Put down a beeper # # Available conditions: # front_is_clear() - Check if front is clear # beepers_present() - Check if beeper is present # facing_north() - Check if facing north main()

Speed: 5

Common Patterns

Here are some common control flow patterns you'll use frequently with Karel:

• Move to wall: Use while front_is_clear(): move()
• Turn right: Call turn_left() three times
• Turn around: Call turn_left() twice
• Clear all beepers: Use while beepers_present(): pick_beeper()

Challenge: Try to modify the code to make Karel collect all beepers in a row, then return to the starting position!