Project 1 Spring 2007

UMBC CS 201, Spring 07

CMSC 201
Programming Project One

Regular Polygons

Out: Monday 2/26/07
Due: Before Midnight, Sunday 3/4/07

The Objective

The objective of this assignment is to get you started writing programs
in C in the UNIX environment. Its main emphasis is design, so we will be
designing the project together in class. This project will also give you
practice writing functions, loops, switch statements and using separate
compilation.

The Background

A REGULAR POLYGON is defined as a
convex polygon with all sides congruent and all angles congruent.
The labeled drawings below show what is meant by the terms: exterior
angle, interior (or vertex angle), central angle,
and diagonal.

Realize that any regular polygon, not just the regular hexagon shown, can
be divided into the same number of triangles as it has sides, with the
base of each triangle being a side of the polygon and that the “tips” of
the triangles join in the center of the polygon.

All formulae shown in the drawings and also those for perimeter and area
shown later are courtesy of
mathwords.com

For all formulae shown:

Names of Regular Polygons

Number of Sides Name
3 Equilateral Triangle
4 Square
5 Regular Pentagon
6 Regular Hexagon
7 Regular Heptagon
8 Regular Octagon
9 Regular Nonagon
10 Regular Decagon

The Task

Design (to be done in class) and code a project that after printing a greeting
to the user which contains information about regular polygons, presents the
user with a nicely-aligned table that shows :

  • the name of the polygon (printed using “%20s”)
  • the number of sides (an integer)
  • the exterior angle in degrees (to 3 decimal places)
  • the sum of the interior angles (an integer)
  • the interior angle in degrees (to 3 decimal places)
  • the number of diagonals (an integer)

for all n-gons from 3 to 10, inclusive. The values in this table may NOT be
hard coded. All of the values in the table MUST be calculated by the
modular functions described in the design.

After presenting the table, your program must direct the user to input the
number of sides of a polygon and the length of the sides. Use this
information to calculate the perimeter and area of that polygon. Display the
name of the polygon with its perimeter and area to the user. Restrict the
user to regular polygons with n of 3 – 10, inclusive. The user should be
allowed to continue to enter polygons as long as s/he wants and should signal
the end by entering the sentinel 0 for n.

Since you are distributing this software to others, you must use separate
compilation and provide the interface for the user. This is in the form of a
well commented header (.h) file. You must have 3 files. The file that
contains main() MUST be called proj1.c; the file containing the
function definitions related to polygons MUST be called polygons.c and
the header file that contains the function prototypes for the functions found
in polygons.c MUST be called polygons.h

You are required to use a switch statement to handle the printing
of the polygon’s names.

You must also check user input for validity and reprompt for a new value
when the user is in error. This should be accomplished in the functions
GetValidNumSides() and GetPositiveValue().

You must adhere to the design given in class. The function prototypes
given below must be used and may NOT be altered in anyway.

void PrintGreeting (void);
void GenerateTable (int min, int max);
void PrintInstructions (void);
int GetValidNumSides (int sentinel, int min, int max);
double GetPositiveValue (void);
void PrintName (int numSides);
double FindExteriorAngles (int numSides);
int FindAngleSum (int numSides);
double FindInteriorAngles (double angleSum, int numSides);
int FindNumDiagonals(int numSides);
double FindPerimeter (int numSides, double side);
double FindArea (int numSides, double side);
double ConvertDegreesToRadians (double degrees);
The following symbolic constants should be used and they should be placed
in your proj1.c file above main():
#define SENTINEL 0
#define MIN 3
#define MAX 10
The following symbolic constants should be used and they should be placed
at the top of your polygons.c file. NOTE: These symbolic constants would
only be placed in the polygons.h file if they were being used by both the
proj1.c and polygons.c files. These are not used in proj1.c. It is okay
to use them within modular functions’ code since they are contained within
the same file AND their values will never change.
#define HALF_ROTATION 180
#define FULL_ROTATION 360
#define PI 3.14159
#define TRIANGLE 3
#define SQUARE 4
#define PENTAGON 5
#define HEXAGON 6
#define HEPTAGON 7
#define OCTAGON 8
#define NONAGON 9
#define DECAGON 10

Where should the function definitions go ?

Most of the functions you are writing for this project deal with polygons
and might be used as modules for future projects. Those function definitions
belong in the polygons.c file and their prototypes in the polygons.h file.

The functions PrintGreeting() and PrintInstructions() are specific to
this project, so their definitions belong at the bottom of the proj1.c file.
Their prototypes belong before main() in the proj1.c file.

Details about the math library

  1. You must #include <math.h>
  2. You must link using the -lm option
  3. The math library does not have a cotangent function, but it does have a
    tangent function called tan(), which takes a double and returns a
    double. You should remember and use the trig identity:
    cot(theta) = 1/tan(theta)
  4. All of the math library trig functions take the angle measurements in
    radians, not degrees, so you’ll have to write the function called
    ConvertDegreesToRadians(), which is a good module to have.

Sample Run with Compilation Shown

linux1[101] ls
polygons.c polygons.h proj1.c
linux1[102] gcc -c -Wall -ansi proj1.c
linux1[103] gcc -c -Wall -ansi polygons.c
linux1[104] gcc proj1.o polygons.o -lm
linux1[105] ls
a.out polygons.c polygons.h polygons.o proj1.c proj1.o
linux1[106] a.out
Your greeting goes here
Table of Regular Polygon Facts
Name # Sides Ext Ang Int Ang Sum Int Ang Diags
Equilateral triangle 3 120.000 180 60.000 0
Square 4 90.000 360 90.000 2
Regular pentagon 5 72.000 540 108.000 5
Regular hexagon 6 60.000 720 120.000 9
Regular heptagon 7 51.429 900 128.571 14
Regular octagon 8 45.000 1080 135.000 20
Regular nonagon 9 40.000 1260 140.000 27
Regular decagon 10 36.000 1440 144.000 35
Your instructions about entering the number of sides
and the length of one side for the calculations of perimeter
and area go here.
Enter number of sides, 0 to quit : 4
Enter the length of one side : 4
Square with sides of 4.000
Perimeter : 16.000
Area : 16.000
Enter number of sides, 0 to quit : 3
Enter the length of one side : 4
Equilateral triangle with sides of 4.000
Perimeter : 12.000
Area : 6.928
Enter number of sides, 0 to quit : 6
Enter the length of one side : 4
Regular hexagon with sides of 4.000
Perimeter : 24.000
Area : 41.569
Enter number of sides, 0 to quit : 2
Sorry 3 – 10 or 0 only
Try again.
Enter number of sides, 0 to quit : 1
Sorry 3 – 10 or 0 only
Try again.
Enter number of sides, 0 to quit : -5
Sorry 3 – 10 or 0 only
Try again.
Enter number of sides, 0 to quit : -1
Sorry 3 – 10 or 0 only
Try again.
Enter number of sides, 0 to quit : 5
Enter the length of one side : 2.5
Regular pentagon with sides of 2.500
Perimeter : 12.500
Area : 10.753
Enter number of sides, 0 to quit : 7
Enter the length of one side : 3.75
Regular heptagon with sides of 3.750
Perimeter : 26.250
Area : 51.102
Enter number of sides, 0 to quit : 8
Enter the length of one side : 25.67
Regular octagon with sides of 25.670
Perimeter : 205.360
Area : 3181.690
Enter number of sides, 0 to quit : 9
Enter the length of one side : 15.29
Regular nonagon with sides of 15.290
Perimeter : 137.610
Area : 1445.214
Enter number of sides, 0 to quit : 10
Enter the length of one side : 17
Regular decagon with sides of 17.000
Perimeter : 170.000
Area : 2223.628
Enter number of sides, 0 to quit : 6
Enter the length of one side : 0
Positive values only! Try again : -3
Positive values only! Try again : 6.2
Regular hexagon with sides of 6.200
Perimeter : 37.200
Area : 99.870
Enter number of sides, 0 to quit : 0
Ending program
linux1[107]

Although your output need not be identical to the above,
all information (including the greeting) must be present.

Please be aware that this is definitely NOT a complete
test of the program. Your testing should be much more extensive.

Submitting the Program

You are to use separate compilation for this project, so you will be
submitting three files.
Your C source code file that contains main() MUST be called
proj1.c. The file which contains the polygon function definitions
MUST be called polygons.c and its header file MUST be
called polygons.h

To submit your project, type the following at the Unix prompt.
Note that the project name starts with uppercase ‘P’.

submit cs201 Proj1 proj1.c polygons.c polygons.h

To verify that your project was submitted, you can execute the
following command at the Unix prompt. It will show all files that
you submitted in a format similar to the Unix ‘ls’ command.

submitls cs201 Proj1

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Monday, 26-Feb-2007 11:00:07 EST

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