Lecture 14:  Arrays

Content Tested:  Writing a program (arrays and functions with array parameters)

Lecture Content:

• Data structures
• Arrays
• Subscripts
• Looping through arrays
• Array arguments and parameters

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:

Notice that this histogram states that two scores are between 90 and 100, 4 scores are between 80 and 89, 1 score is between 50 and 59, 1 score is between 40 and 49, 2 scores are between 30 and 39, and 1 score is between 10 and 19.

Be sure that when planning your solution, you make use of an array and multiple functions.

Just like the other exercises, it is important to proceed with the following steps:  program specification, the algorithm and basic design of the program, and then the implementation of the C code.  When you have finished the coding portion, be sure to test your program on some sample input.

Problem Specification:
 
 
 
 
 

The Algorithm:
 
 
 
 
 
 
 

The C Program:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Possible Solution

/* prototypes */
void read_values (int grade[], int grade_size);
void print_histogram (int grade[], int grade_size);
void print_X (int num_X);

int main (void) {

  /* declarations */
  int grade_hist[10] = {0,0,0,0,0,0,0,0,0,0};
  /* zero out the histogram which keeps counts of grades in each range of
     ten, grade[0] represents the number of grades between 0 and 9,
     grade[1] represents the number of grades between 10 and 19, etc.
  */

  read_values (grade_hist, 10);
  print_histogram (grade_hist, 10);

  return 0;
}

/* read_values */
/* parameters: int grade[], int grade_size */
/* notice that grade[] will be passed by reference, so any updating done
   by this function will remain when the function returns */
/* return: void (we will update the array grade[] */
/* functionality: reads grades entered by user and increments the appropriate
   10's location in the array grade[] */

void read_values (int grade[], int grade_size) {

  /* declarations */
  int current_grade;              /* current grade entered by user */

  /* prompt user to enter grade */
  printf("Please enter a grade: ");
  scanf("%d", &current_grade);

  while (current_grade != -1) {
    /* note here that -1 is a sentinel value */
    /* increment appropriate bin in grade[] */
    current_grade = current_grade / 10;   /* gives bin number */

    if (current_grade == 10) {
      /* we must put this in location 9 of array instead of location 10 since
       location 10 is off the end of the array */
      grade[9]++;       /* increment the count at location 9 */
    }

    else {
      grade[current_grade]++;  /* increment the count for the current tens */
    }
    /* read new grade */
    printf("Please enter a grade: ");
    scanf("%d", &current_grade);
  }
}

/* print_histogram */
/* parameters: int grade[], int grade_size */
/* return: void */
/* functionality: this function prints the histogram in the format of high
   scores to low scores */

void print_histogram (int grade[], int grade_size) {

  /* declarations */
  int i;                      /* looping variable */

  /* top bin is different from the rest since it goes from 90 to 100, so
     we will print this outside the loop */

  printf("90 - 100: ");
  print_X(grade[9]);          /* print appropriate number of X's */
  printf("\n");

  for (i = 8; i >= 0; i--) {  /* go in reverse order of grade array indices */
    printf("%d0 - %d9: ", i, i);
    print_X(grade[i]);
    printf("\n");
  }
}

/* print_X */
/* parameters: int num_X */
/* return: void */
/* functionality: prints num_X number of capital X's on a single line
   not followed by a newline */

void print_X (int num_X) {

  /* declarations */
  int i;                      /* looping variable */

  for (i = 0; i < num_X; i++){
    printf("X");
  }
}
 

Possible Uses of Activity:

• Have students work in groups to come up with the algorithm and then write the program as a class.
• As a class, discuss the algorithm and functional decomposition.  Have each group write a separate function so they see the need for formal function specifications.  If one group does not adhere to the specifications, then the entire program won't work correctly.  Another function that the instructor could add would be zero_histogram which would place 0's in every position in the histogram.  The above program does this in the initialization of the histogram.
• The instructor might want to extend this activity by asking the following questions:
• Suppose the instructor wants a more detailed picture of the scores and wants bin sizes of 5 instead of 10.  What parts of the program need to be changed?
• There are too many students in the class to display one X for each score.  Suppose now that one X represents 5 students with scores in the same bin.  What would you need to change in the program?  (Detail:  if 5 - 9 students score in the same bin, only 1 X will appear for this case.  Only after the 10th student will a second X appear.)
• The instructor wants some additional functionality in the program.  In addition to displaying a histogram of the scores, the instructor wants the program to display the minimum score, the maximum score, and the average score for the class.  Where would you keep track of this information?  Would you design new functions?  Do you now need to store all the scores entered by the user? (hopefully the answer will be no)