CS-182 Lab 3: Writing a Program

Dr. Mark J. Sebern

Overview

The purpose of this lab is to design and implement a stand-alone "console mode" program that incorporates at least one function in addition to main().

Activities

In this lab, you will:

• Design a program to satisfy a problem statement
• Write, compile, build, and test the program
• Report on your results

Problem statement

You have been asked to design and implement a C++ program to calculate the area of a triangle, given the 2-dimensional coordinates of its vertices. Your program must also output some additional information.

Your program will be given the x- and y-coordinates of the three triangle vertices. It should output:

• The coordinates of the three vertices
• The distances between pairs of vertices (lengths of the triangle sides)
• The height of the triangle (from vertex 3 to the base specified by vertices 1 and 2)
• The area of the triangle

Graphically, the problem looks like this:

The distance between two points (a and b) is given by:

The distance from a point p to a line with endpoints a and b is given by:

Read the input from a text file named "lab3in.txt"; write the output to a text file named "lab3out.txt". For a simple test case, the input might look like this:

0 0        
3 0
6 4 

The corresponding output file would be:

Your program output should match the format of the sample output file. If you wish, you may enhance the program (e.g., format the output so numbers line up and have a consistent width), but be sure you meet the problem specifications first. You may round off all printed answers to two decimal places, and assume that no coordinate value magnitude will exceed 999.99.

Detailed instructions

If you have difficulties with any part of the lab, consult the instructor for assistance. The basic sequence is:

1. Working with one or two other students, sketch out a design solution:
   • Identify the objects needed in your program.
   • Specify the attributes and behaviors of the objects.
   • Incorporate functions to implement parts of the calculation. For example, you might calculate the distance between two points and the distance from a point to a line using functions with the following prototypes:

     double Distance (double xa, double ya, double xb, double yb);
     // Arguments:
     //     xa  - X-coordinate of the first point.
     //     ya  - Y-coordinate of the first point.
     //     xb  - X-coordinate of the second point.
     //     yb  - Y-coordinate of the second point.
     // Returns: The magnitude of the distance between the two points.
     
     double LineDistance (double xp, double yp,
                          double xa, double ya,
                          double xb, double yb);
     // Arguments:
     //   xp - X-coordinate of the point.
     //   yp - Y-coordinate of the point.
     //   xa - X-coordinate of the origin of the line segment.
     //   ya - Y-coordinate of the origin of the line segment.
     //   xb - X-coordinate of the end of the line segment.
     //   yb - Y-coordinate of the end of the line segment.
     //   ASSUME: The length of the line segment is not zero.
     // Returns: The magnitude of the perpendicular distance
     //          between the point and the line containing
     //          the line segment.

   • Document your design clearly.
   • Develop at least 4 test cases for your program, and list the input data and expected output values for each.
2. Working on your own, write the program (source code) to implement your design.
3. Test the program by running it and supplying input values from the test cases developed above.
4. Submit the lab report (details below).

Lab report

The lab report should consist of the following:

• The design documentation, and the names of the students who contributed to it.
• The source code for your program.
• The program output for the following test case:
  • Point 1: (-2.0,5.0)
  • Point 2: (0.598,6.5)
  • Point 3: (0.33, 10.964)

• A brief description of any problems you encountered or questions you have regarding the lab.

You may submit this report in hard-copy form, or email it to the instructor. If you choose email, it may be convenient to put the textual portion of the report directly in the message, and to attach the other files. Ask the instructor for the details on this procedure if you wish to try it. Be sure to keep copies of all your files, in case something gets lost; it may be wise to keep a diskette backup as well.

The lab report is due by the beginning of the following lab period, though you are encouraged to submit it sooner if you can. Your grade will depend on quality of design and clarity of the code and documentation, as well as whether your program produces the correct results. If you have any questions, consult the instructor.

This page was last updated on October 08, 1997; send comments to Mark Sebern.