📓2.11: Nested Iteration

Table of Contents

• Nested For Loops
  • Nested Loops with Turtles

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📖 This page is a condensed version of CSAwesome Topic 2.11

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Nested For Loops

A nested loop has one loop inside of another. These are typically used for working with two dimensions such as printing stars in rows and columns as shown below:

When a loop is nested inside another loop, the inner loop runs many times inside the outer loop. In each iteration of the outer loop, the inner loop will be re-started.

The inner loop must finish all of its iterations before the outer loop can continue to its next iteration!

💬 DISCUSS: What does the following code print out? Watch the code run in the Java visualizer.

Notice how the inner loop is started over for each row. Can you predict how many rows and columns of stars there will be?

for (int row = 1; row <= 3; row++) {
    for (int col = 1; col <= 5; col++) {
        System.out.print("*");
    }
    System.out.println();
}

Can you change the code to print a rectangle with 10 rows and 8 columns of stars? You can also try replacing line 10 with this print statement to see the rows and columns: System.out.print(row + "-" + col + " ");

Nested Loops with Turtles

❄️ Try nested loops with Turtle objects to create a snowflake design!

💻 In-Class Activity: Turtle Snowflakes

1. Go to
2. Make sure you SIGN IN!
3. Complete the Programming Challenge: Turtle Snowflake activity in pairs.

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Acknowledgement

Content on this page is adapted from Runestone Academy - Barb Ericson, Beryl Hoffman, Peter Seibel.