When a loop is placed entirely within the body of another loop, it is called nested iteration. AP CSA Topic 2.11 focuses on tracing nested loops, determining execution counts, and understanding how the inner loop behaves for each iteration of the outer loop.

In this interactive practice set, you will work through 10 multiple-choice questions covering nested loop execution, dependent loop bounds, tracing, and output patterns.

Key Concepts to Remember Before You Start:

• Total Executions: If the outer loop runs x times and the inner loop runs y times independently for each outer iteration, the inner statement executes x × y times.
• Resetting the Inner Loop: The inner loop starts again from its initialization whenever the outer loop begins another iteration.
• Dependent Bounds: If the inner loop's boundary or initialization depends on the outer loop's variable, the number of inner-loop executions can change from one outer iteration to the next.

Test your knowledge with the interactive quiz below. Careful tracing is required—work through the values of both loop variables systematically.

for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 4; j++) {
        System.out.print("*");
    }
}

for (int r = 1; r <= 3; r++) {
    for (int c = 1; c <= r; c++) {
        System.out.print(c + " ");
    }
    System.out.println();
}

int count = 0;

for (int x = 1; x <= 5; x++) {
    for (int y = 5; y > x; y--) {
        count++;
    }
}

System.out.println(count);

int total = 0;

for (int i = 0; i < 2; i++) {
    for (int j = 1; j < 4; j++) {
        total += (i + j);
    }
}

System.out.println(total);

for (int a = 1; a <= 3; a++) {
    int b = 1;

    while (b <= 2) {
        System.out.print(a + "" + b + " ");
        b++;
    }
}

int k = 0;

for (int i = 0; i < 5; i++) {
    for (int j = 0; j < 5; j++) {
        if (i == j) {
            k++;
        }
    }
}

System.out.println(k);

int sum = 0;

for (int i = 0; i < 3; i++) {
    for (int j = i; j < 3; j++) {
        sum++;
    }
}

System.out.println(sum);

for (int i = 0; i < 5; i++) {
    for (int j = 0; j < 5; j++) {
        if (i + j == 4) {
            System.out.print("X");
        } else {
            System.out.print("O");
        }
    }
    System.out.println();
}

int n = 4;
int result = 0;

for (int i = 0; i < n; i++) {
    int p = 1;

    for (int j = 0; j <= i; j++) {
        p *= 2;
    }

    result += p;
}

System.out.println(result);

Why Nested Iteration Matters for AP CSA

Nested iteration requires you to trace an inner loop while keeping track of the current value of the outer-loop variable. The number of inner-loop executions may remain constant or may change depending on the outer-loop value.

The same tracing skills are useful when working with rows and columns of two-dimensional arrays later in Unit 4: Data Collections. Being comfortable with nested loops will help you follow algorithms that process multiple dimensions of data.

Continue Your AP CSA Practice

After practicing nested iteration, continue with the other Unit 2: Selection and Iteration topics.

Review the Unit 2 Selection & Iteration Practice Assessment for additional mixed practice covering the currently available iteration topics.