Lecture 10:  Loops

Content Tested:  Programming with loops

Lecture Content:

• Loop design and development
• Code reuse

Goals:

• Ability to synthesize and integrate information
• Learn concepts and theories
• Develop capacity to think for oneself
• Develop ability to think creatively

Assessment Technique:  Programming Activity

Purpose:

Activity:

     *
    ***
     *
    ***
   *****
     *
    ***
   *****
  *******
     |
-----+-----

Note that the tree consists of drawing spaces, stars, a vertical line, a plus sign, and minus signs.  Write a function called print_tree that takes as a parameter the size of the tree.  The size is the number of tiers (or triangles) that make up the tree.  In the above picture, there are 3 tiers.  You may assume that the size of the tree is greater than or equal to 1.

Hints:
1.  Before diving into the code, be sure to design your algorithm -- think about how many spaces and stars are required to print one tier of the tree.
2.  Think about writing a separate function called print_tier that simply prints a single tier of the tree given the number of rows and the center position for the tier.
3.  Use the entire design process -- problem specification, algorithm, function design, implementation, and testing.

Possible Solution

void print_tree(int size){

  int i;                 /* looping variable */

  /* print tiers */
  for(i = 0; i < size; i++){
    print_tier(size, i+2);
  }

  /* print trunk */
  for(i = 0; i < (size + 2); i++){
    printf(" ");
  }
  printf("|\n");

  /* print ground */
  for(i = 0; i < (size + 2); i++){
    printf("-");
  }
  printf("+");
  for(i = 0; i < (size + 2); i++){
    printf("-");
  }
  printf("\n");
}

/* print_tier
 * input:  int size, int num_rows
 * output:  none
 * function:  prints a single tier consisting of a triangle
 * with num_rows rows.  size indicates the centering position
 * of the tier (number of spaces over where tip should start)
 */

void print_tier(int size, int num_rows){

  /* tree is centered size + 2 spaces from the left */
  int i, j;

  for(i = 0; i < num_rows; i++){
    /* space over size + 2 - i spaces */
    for(j = 0; j < (size + 2 - i); j++){
      printf(" ");
    }

    /* print i * 2 + 1 stars */
    for(j = 0; j < (i * 2 + 1); j++){
      printf("*");
    }
    printf("\n");
  }
}

Possible Uses of Activity:

• Break students into small groups (2-4 people) and have each group work on the activity.  Encourage one or more groups to present their solution to the rest of the class (If groups write their code on transparency slides, showing the class the code is very easy since it eliminates the time for writing code on the blackboard or on a blank slide on the overhead projector.)  If the instructor sees an error in the program, point it out and ask the rest of the class how one might fix the error and its type (syntax vs. semantic).
• If groups come up with for and while loops, this might be a good time to explain to the class when for loops are appropriate and when while loops are appropriate.
• Break the students into 2 groups.  Have 1 group work on the print_tree function and the other work on the print_tier function.  This will require communication between the groups regarding the exact parameters to the print_tier function.