Latest Revision: August, 2007
Directions for Lab #2
Read and study all these directions before the day of the lab. Try to
rehearse mentally what you will be doing. Better still, if you have time, get
online and actually rehearse some of the steps.
The goal of this exercise is to develop an interactive program
that uses integer arithmetic operations.
A Pythagorean triple is a set of three positive integers that represent the
sides of a right triangle. Such triples -- X, Y, Z -- satisfy the relation:
X*X + Y*Y = Z*Z
-- which means: "The square of X plus the square of Y equals the square of Z."
You can generate ("make") Pythagorean triples by using the following algorithm
(recipe):
First pick any two positive integers M and N with M > N, then determine the
lengths of the sides of a right triangle like this:
Side One = M*M - N*N
Side Two = 2*M*N
Hypotenuse = M*M + N*N
Lab02.cpp contains the shell of an interactive program that reads values for M
and N, with M > N, and calculates a Pythagorean triple. Below is an example
interactive session. The characters entered by the user of the program are
shown underlined and in boldface.
john@vega: a.out
Program to Calculate Pythagorean Triples
Enter an integer N: 2
Enter an integer M > N: 5
Pythagorean Triple
Side One = 21
Side Two = 20
Hypotenuse = 29
john@vega:
File Lab02.cpp is as follows:
//
// lab02.cpp. This program reads two positive integers
// M and N with M > N and displays a Pythagorean triple,
// which consists of three positive integers that represent
// the sides of a right triangle.
//
#include <iostream>
using namespace std ;
int main(void)
{
/* ***a*** Declare M and N and comment on their meanings */
/* ***b*** Display: Program to Calculate Pythagorean Triples */
/* ***c*** Prompt and read a positive integer N */
/* ***c*** Prompt and read a positive integer M > N */
/* ***b*** Display: Pythagorean Triple */
/* ***d*** Calculate and display Side one */
/* ***d*** Calculate and display Side two */
/* ***d*** Calculate and display Hypotenuse */
return 0;
}
Individual steps:
- Save a copy of the lab02.cpp shown above as a file. Give the
file the same name: lab02.cpp. To make the file you can just
select the program text, copy it, paste it into a window running an
editor, and save it.
- Below the ***a*** comment insert a declaration of integer variables M and
N and comment on their meanings. (See your C++ textbook for examples of
this kind of declaration.) Save, compile and execute the program.
Correct any errors.
- Below each ***b*** comment insert an output statement -- one to display
"Program to Calculate Pythagorean Triples" and one to display
"Pythagorean Triple". Construct the statements so that the program
output will be just as in the example interactive session shown above.
Make sure that your code creates blank lines just as in the example.
Re-run the program (i.e. save, compile and execute it again). Correct
any errors. Notice the output you get.
- Under the ***c*** comments insert code to request and read
the integers N and M. Construct the code so that the
program will behave just as in the example interactive
session. (Notice that each prompt is indented in that
example.) Re-run the program. Correct any errors. Notice
the output you get.
- Under each ***d*** comment put the code for the appropriate
output statement. Construct the code, so that the program
will display the Pythagorean triple corresponding to the
values of N and M that were input. The numbers output must
be M*M-N*N, 2*M*N, and M*M+N*N.
Get the indentation (spacing) right, as in the
example.
Don't use any new variables for this part of the code.
Perform the computations in the output statements. (As an
example of the general idea: cout << 3*A+6*4 <<
endl; is an output statement that computes 3A+24 and
outputs it without using any new variables.)
Re-run the program. Correct any errors. Notice the output you get.
Verify that the numbers in the output do form a Pythagorean triple. For
example, if the output contains the numbers 21, 20, and 29, then verify
using a calculator (or pencil and paper) that 21*21 + 20*20 = 29*29.
(This is a critical step! The whole point of learning to program is to
make the computer give us what we want. The output has to be correct!)
- Run the program and enter numbers that violate the directions in the
following way: Enter one negative integer and one positive one. Does
the program produce a Pythagorean triple? Refer to the program code.
Can you point out what made the program succeed or fail?
- Run the program and enter numbers that violate the directions in a
different way: Enter two positive numbers but have M < N. Does the
program produce a Pythagorean triple? Refer to the program code. Can
you point out what made the program succeed or fail?
- Make a script (you could call it lab02.script) where you run the program
and enter 3 and 7 for N and M. Refer to the directions of the
"Hello World! assignment"
if you need help with the directions for making a script.
- E-mail me a copy of the program source code (the file lab02.cpp) with
subject line:
CS1500Lab02Source
E-mail me a copy of the script with subject line:
CS1500Lab02Script
(A word about the subject lines - it is really extremely important that
you use the exact subject lines I specify. This will assure that I am
able to find your message among the hundreds and hundreds that I
receive each day. You will lose a significant amount of credit for this
assignment if you don't use the correct subject line. The easiest way to make sure you are using the
correct subject line is to just select, copy, and paste it into the
appropriate location when you are composing the e-mail.)
You may refer to the directions of the
"Hello World!" assignment if you need help with sending the
e-mail. Also feel free to just ask someone - including me.