Discuss and explore the difference between additive (sequential) and multiplicative (nested) loop structures to give students practice reasoning about loops.

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  • Look out for this common misconception: Students, mistakenly, believe that nested loops are loops that run in parallel.
  • Example 1: The following Java code uses an additive loop structure:
    for (int p=0; p<=n; p++) {
      System.out.println(“Hello!”);

    }
    for (int r=0; r<n; r++) {

      System.out.println(“Hello!”);

    }

    • In this example, the first loop executes in its entirety before the second loop begins.
  • Example 2: The following Java code uses a multiplicative loop structure:
    for (int p=0; p<=n; p++) {
      for (int r=0; r<n; r++) {
        System.out.println(“Hello!”);

      }

    }

    • In this example, the inner loop must fully execute before p can be incremented.
External Source: 

Leigh Ann Sudol-DeLyser’s notes from 2009 AP CS A exam.

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