CS 1500-2, Spring 2009

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. Lab 2

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 -- A, B, C -- satisfy the relation:

-- which means: "The square of A plus the square of B equals the square of C."A*A + B*B = C*C

For more information about Pythagorean Tripples:

MathWorld

Wikipedia

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:

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

Side One = M*M - N*N

Side Two = 2*M*N

Hypotenuse = M*M + N*N

mmartin@vega: g++ lab02.cppmmartin@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

mmartin@vega:

//

// 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;

}

- 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.

- Upload your source code (lab02.cpp) and your script
(lab02.script) to the CSHomework
system.

Based on an assignment created by Dr. Sarraille.