Homework 2 Solution


Category: Tag:


Use the handin directory hw2 to submit your work

Shape editor

Note: the concepts and software developed in Homework2 may be used in Homework3.


In this assignment you will write a program that manipulates geometric shapes.

We will consider the following set of shapes, named O, I, L, S, X, U (the names are reminiscent of the shapes). We can represent shapes by drawing the squares forming the shape as shown in Figure 1:

Figure 1

The cells (or squares) forming a shape are indexed by a number starting from 0, as shown in Fig

  1. A shape can be placed on a board by specifying the position of its “zeroth cell” in the x-y plane. In Figure 2 below, shapes have been placed on a board as follows:

Figure 2

  • A shape of type “L” placed at (0,7)

  • A shape of type “L” placed at (5,8)

  • A shape of type “I” placed at (9,6)

  • A shape of type “X” placed at (5,4)

  • A shape of type “O” placed at (8,5)

  • A shape of type “U” placed at (0,2)

  • A shape of type “O” placed at (1,0)

  • A shape of type “S” placed at (4,0).

  • A shape of type “S” placed at (7,1).

HW2 Assignment

The goal of HW2 is to implement classes representing shapes. A given program will use this class to create shapes at arbitrary locations in the x-y plane and move them. The program uses a function to move shapes and to detect if shapes overlap. The board is assumed to be the entire x-y plane.

The class Shape is an abstract base class from which six classes are derived, named: O, I, L, S, X, U. A detailed specification of the class Shape is given below. You are given the header file Shape.h (at http://web.cs.ucdavis.edu/~fgygi/ecs40/homework/hw2). Your task is to write the implementation file Shape.cpp containing the implementation of all classes. You are not allowed to modify the file Shape.h (Do not insert your name or SID in it since we will use the

cmp command to check that the file is the same as the original). Your class implementation file Shape.cpp should compile without warning using the command

$ g++ -Wall –c Shape.cpp

You are also given a program testShape.cpp and a Makefile (same web site as above). These two files should not be modified. The testShape.cpp program tests the functionality of the Shape class. You should be able to build the executable testShape using the command

$ make

You will use the testShape executable and the input and output test files provided on the web site to check the functionality of your classes and verify that your program reproduces the test output exactly. Use the diff command to compare your output file with the output file provided. Note that these test files do not check all the functionality and you are responsible for verifying your implementation. Other test files will also be used when grading your implementation. The testShape program reads input from stdin and writes to stdout. It can be used e.g. as

$ ./testShape < test1.in

It can be assumed that input will consist of two lines. Each line consists of one character followed by two integers. The character and integers are separated by white space as in e.g.

X2 -3

Specification of the Shape class

We describe here the detailed specification of the Shape class. The positions of the cells occupied by a shape are stored in two integer arrays whose size depends on the shape, i.e. a shape occupies the cells located at (x[0],y[0]), (x[1],y[1]), etc…

Study carefully the file Shape.h. Some members are public and some protected. Some members are virtual. Make sure you understand why. Study the file testShape.cpp in order to understand how the classes will be used.

Public members

virtual char name(void) = 0;

This pure virtual function returns the name of the class instance as a character, i.e. O, I, L, S, X, U.

void print(void)

This function prints information about the location of the shape by showing the position of the cells that the shape occupies:

name at (x[0],y[0]) (x[1],y[1]) …

For example, from Figure 2:

X at (5,4) (4,5) (5,5) (6,5) (5,6)

bool overlap(const Shape &s)

This function should return true if the shape calling the function overlaps with the shape s.

This can be checked by comparing the arrays x and y of both shapes. If there is no overlap, i.e.

no cells are shared by the two shapes, the function should return false.

void move(int dx, int dy)

This function moves the shape by a displacement (dx, dy). This function modifies the values of the arrays x and y. Note that this function is the same for all shapes and need not be implemented as a virtual function.

static Shape *makeShape(char ch, int posx, int posy)

This function is a “shape factory”. It is used to generate instances of shapes. It creates an instance of the appropriate kind of shape (specified by the character ch, with values ‘O’, ‘I’, ‘L’, ‘S’,‘X’, ‘U’) at the given position (posx,posy) using the operator new, and returns a pointer to the instance. If the character ch is not one of the allowed letters, the function should throw an invalid_argument exception. The error printed by the program should correspond to the example given in one of the test files.

protected members

int *x,*y

The arrays holding the coordinates of the cells occupied by the shape.


Create a tar file named hw2.tar containing the files Shape.h, Shape.cpp, testShape.cpp and Makefile. Do not compress the tar file. The files Shape.h, testShape.cpp and Makefile must be identical to the files provided. Include your name and Student ID in a comment at the top of the Shape.cpp file. Submit your project using:

$ handin cs40 hw2 hw2.tar

error: Content is protected !!