Lecture 9:  Iteration

Content Tested:  Writing a simple program

Lecture Content:

• Iteration
• Loops and Nested Loops
• While statements
• For statements

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:

Suppose you and a friend both work at the local grocery store.  The boss gives you two choices of how you will be paid.  Here are the choices:

Choice 1:  The boss will pay you 1 cent the first day, 2 cents the second day, 4 cents the third day, 8 cents the fourth day, and so on.  Each day your salary will be double of your previous day's salary.

Choice 2:  The boss will pay you $50.00 per day.

Since you want to make the most money, you decide to write a C program that calculates the number of days you need to work for Choice 1 to be better than Choice 2.  Suppose you take Choice 1 and your friend takes Choice 2.  Write the necessary C code to print out the number of days you need to work in order for your total salary to surpass your friend's total salary.  Like all programs, it is necessary to solve the steps of formulating the problem and describe the algorithm.

Problem Specification:
 
 
 
 
 

The Algorithm:
 
 
 
 
 
 
 

The C Program:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Possible Solution

int main (void) {

  /* declarations */
  int num_days = 0;           /* total number of days necessary to
                                 earn more money by doubling salary */
  int today_price = 1;        /* in cents, today's pay for the doubling
                                 salary */
  int friend_price = 5000;    /* in cents, the day's pay for the friend */
  int my_total = 0;           /* in cents, my total salary */
  int friend_total = 0;       /* in cents, my friend's total salary */

  while (my_total <= friend_total) {
    my_total = my_total + today_price;
    num_days = num_days + 1;
    today_price = today_price * 2;     /* prepare for tomorrow's pay */
    friend_total = friend_total + 5000;   /* make sure friend gets paid */
  }

  printf("The number of days is: %d\n", num_days);
 

  /* return successfully */
  return 0;
}

Solution using dollars:

int main (void) {
 
  /* declarations */
  int num_days = 0;           /* total number of days necessary to
                                  earn more money by doubling salary */
  double today_price = .01;   /* in dollars, today's pay for the doubling
                                  salary */
  double friend_price = 50.0; /* in dollars, the day's pay for the friend */
  double my_total = 0.0;      /* in dollars, my total salary */
  double friend_total = 0.0;  /* in dollars, my friend's total salary */

  while (my_total <= friend_total) {
    my_total = my_total + today_price;
    num_days = num_days + 1;
    today_price = today_price * 2.0;     /* prepare for tomorrow's pay */
    friend_total = friend_total + 50.0;  /* make sure friend gets paid */
  }

  printf("The number of days is: %d\n", num_days);
 

  /* return successfully */
  return 0;
}

Possible Uses of Activity:

• Have students work in groups to come up with the algorithm and then write the program as a class.
• 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).