Lesson 6E Nested Loops. By John B. Owen All rights reserved 2011, revised 2014

Transcription

1 Lesson 6E Nested Loops By John B. Owen All rights reserved 2011, revised 2014

2 Table of Contents Objectives What are nested loops? Examples: #1 x Box #2 y Box #3 starbox #4 box method #5 triangle #6 reverse triangle #7 pyramid #8 inverted pyramid #9 hollow box #10 checkers Lesson Summary / Labs Contact Information for supplementary materials

3 Objectives In this lab you will learn about nested loops, which are useful in several ways. They can create interesting output patterns, and are essential in managing matrices (twodimensional arrays) which will be covered in Lesson 8. Nested loops are also used in several sorting algorithms, such as the selection, bubble, and insertion sorts.

4 What are nested loops Nested loops are two loops, one nested inside the other. The first loop is called the outside loop, sometimes called the row loop. Its primary job is to set out the number of rows for the pattern.

5 What are nested loops The second loop, the column loop, is nested inside the first one, and has the job of controlling the process for each row.

6 Nested Loop example #1 Here is the sequence of events for this example x, the loop control variable of the first loop, starts at 0

7 Nested Loop example #1 While x has a value of zero, the second loop makes a complete cycle with y going from zero to 4, effectively outputting the value of x five times.

8 Nested Loop example #1 As x steps through the values 1, 2, and 3, the second loop variable cycles from zero to 4 each time, again outputting the x value five times on each row.

9 Nested Loop example #2 This second example has the exact loop structure as the first, but this time, y is the output value. Check out the difference.

10 Nested Loop example #2 You can see that a complete inside loop cycle is output each time the outside loop takes a single step.

11 Nested Loop example #3 In this example, a star ( * ) is output each time, creating a 4X5 box pattern.

12 Nested Loop example #4 Here a method called box is defined, receiving two integer parameters, representing the height and width of a box pattern. It is then called three times to create an interesting composite pattern.

13 Nested Loop example #5 Here a method called triangle is defined. Study this one carefully and see if you can figure out what is happening to create the triangle pattern.

14 Nested Loop example #5 Here is how it works: The outside loop is the same as before, establishing how many rows will be created. The inside loop is different

15 Nested Loop example #5 It still starts at zero, but the CHECK of the loop is different. Instead of using the value of side, it uses the changing value of x, creating the triangle effect.

16 Nested Loop example #5 As the value of x increases, the number of steps for the inside loop also increases accordingly. When x is zero, the inside loop has exactly one step.

17 Nested Loop example #5 When x has the value 1, the inside loop takes two steps. When x is 2, y takes three steps, and the triangle output is complete.

18 Nested Loop example #6 Here we have a reverse triangle, which requires two inside loops, one to create the indented spaces, and the second to create the star pattern.

19 Nested Loop example #6 The outside loop is the same as in previous examples, responsible for establishing the total number of rows.

20 Nested Loop example #6 The first inside loop creates blank spaces to indent the output, first creating two spaces on the first row, one on the 2nd, and none on the third.

21 Nested Loop example #6 The second inside loop immediately follows the first inside loop with the correct number of stars for each row, first one, then two, then three.

22 Nested Loop example #7 This one creates a pyramid by adapting the reverse triangle method. Can you spot the change in the code?

23 Nested Loop example #8 Here is an inverted pyramid, with a slight modification from the pyramid method. Check it out!

24 Nested Loop example #9 This is a hollow box. The original box method is modified for this one. Notice how the if else statement is used to control the output.

25 Nested Loop example #10 Another adaptation of the box method creates this interesting checkerboard pattern.

26 Lesson Summary The possibilities for nested loop output patterns are numerous, only limited by your imagination and ability to produce what you imagine. In all of the examples shown here, the nested loop structure was similar outside loop to control the rows, inside loop to control the columns.

27 Lesson Summary Once you understand how to control these aspects of nested loops, the various outputs are just modifications and adjustments of them. Now it is time to practice some more output patterns.

28 Labs NestedLoops will be the name of this series of labs. As you did before, create a separate folder and file called NestedLoops and do your work there. The first task is simply to duplicate all seven of the methods shown in this lesson.

29 Labs Then you are asked to create some new methods using nested loop patterns. You may use any previously defined methods to create these new ones.

30 Lab 6E1 box WAM called box that will receive two integer parameters for the rows and columns and output a box star pattern (see example #4 on slide 12).

31 Lab 6E2 triangle WAM called triangle that will receive one integer parameter and create a triangle star pattern (see example #5 on slide 13).

32 Lab 6E3 reversetri WAM called reversetri that will receive one integer parameter and create a reverse triangle star pattern (see example #6 on slide 18).

33 Lab 6E4 pyramid WAM called pyramid that will receive one integer parameter and create a pyramid star pattern (see example #7 on slide 22).

34 Lab 6E5 invertedpyramid WAM called invertedpyramid that will receive one integer parameter and create an inverted pyramid star pattern (see example #8 on slide 23).

35 Lab 6E6 hollowbox WAM called hollowbox that will receive two integer parameters and create a hollow box star pattern (see example #9 on slide 24).

36 Lab 6E7 checkers WAM called checkers that will receive two integer parameters and create a checker board star pattern (see example #10 on slide 25).

37 Lab 6E8 reflectedpyramid WAM that will receive one integer parameter and create reflected pyramid shape, as shown below.

38 Lab 6E9 hourglass WAM that will receive one integer parameter and create an hour glass shape, as shown below.

39 Lab 6E10 diamond WAM that will receive one integer parameter and create a diamond shape, as shown below. Note: this is DIFFERENT from lab 6E8.

40 Lab 6E11 doubleborderbox WAM that will receive two integer parameters and create a hollow box with a double star border.

41 Lab 6E12 hollowdiamond WAM that will receive one integer parameter and create a hollow diamond.

42 JavaDoc Complete the documentation for all of the methods, and run the JavaDoc utility.

43 CONGRATULATIONS! You now know how to create several interesting patterns using nested loops! Lesson 7A will continue the study of arrays.

44 Thank you, and have fun! To order supplementary materials for all the lessons in this package, such as lab solutions, quizzes, tests, and unit reviews, visit the O(N)CS Lessons website, or contact me at John B. Owen