Project 3

Due: Thursday, April 10 1997

Objective

The objective of this assignment is to give you practice using loops, conditionals, and switch. You are also required to write at least one function other than main(). A logical choice might be a procedure called PrintOneImage.

Assignment

The X Files team has recently received a secret transmission from outer space, which they have stored in a file. They know that this file is actually a sequence of images. Each image has been encoded as a sequence of positive integers terminated with a -1. The overall sequence of images found in a file is terminated with a final -1.

You have been asked to help the X team by decoding these images and displaying them on the crude but serviceable non-graphical computers to which you have access.

Before dying of unknown causes, the radio telescope technician who received the mysterious broadcast revealed the following facts:

• Each image is rectangular.
• Each image has at least one column and one row.
• The first integer in the image representation is the number of columns.
• Subsequent integers represent the light intensity at a given point or pixel.
• A pixel is represented by an integer between 0 and 255.
• The end of the image is marked with a -1.
• The last image of the file is marked with an additional -1.
• The pixels are listed a row at a time, from left to right within a row and the rows are given from top to bottom. Thus the first pixel given is the one in the upper left-hand corner of the image and the last is for the lower right-hand corner.

Since your project is not well supported by the Agency's upper management, you will have to make do with whatever tools you have available. These include a VT100 terminal which has no capability to display graphical images. You do, however, have a C compiler and, luckily, have just then begun to learn how to use it in your studies at UMBC. You could write a program to interpret the images and display them crudely on the terminal using "ASCII graphics".

You can translate the pixel values into printable characters using the following conversion chart:

value range char name -------------------------------- 0 - 31 space 32 - 63 . period 64 - 95 ' apostrophe 96 - 127 - dash 128 - 159 : colon 160 - 191 | vertical bar (pipe) 192 - 223 \ backslash 224 - 255 @ at sign Notice that the intensity of the printed characters (amount of ink used) increases as the integers increase. The intensity of each pixel is the integer representing that pixel. (Hint)

In addition to printing each image, your program must also calculate and display for each image (1) the total number of pixels in the image, (2) the number of rows of pixels in the image, and (3) the average intensity of the pixels.

Example File and Corresponding Image

The file would produce the following image: FILE IMAGE ----------------------------- 5 200 199 201 210 205 \\\\\ 0 99 2 99 4 - - 240 3 245 2 250 @ @ @ 1 98 96 99 0 --- -1 -1

Using a file as input

You will be using a powerful feature of the Unix operating system known as "file redirection" to read from the file. This will allow you to read an integer at a time from the file using the familiar GetInteger() function, just as if the user was typing one integer at a time from the keyboard. The only difference is that you don't have to prompt the user for input.

To run your program using one of the data files, for this project as input, use the following command:

a.out < ~sbogar1/201/test1.dat
OR you could save the data files into your own account from netscape and then use redirection of your own local copy of a data file, using the command:
a.out < test1.dat
There are several sample data files in place now. The actual secret data is being kept in a secure place and is heavily encrypted. It will be made available to you later.

If you need help

If you are having problems seek help as soon as possible. You can ask questions during the discussion meeting, visit the Computer Science Help Center, see your TA or the Instructor.

What to turn in

When you are sure that your program is properly documented and that it is working correctly, you should submit your project using the submit command as you did for earlier projects.