CSC231 Homework 6 2015

--D. Thiebaut (talk) 10:46, 4 November 2015 (EST)

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This homework is due on Wednesday 11/11/15, at 23:55 p.m.

Problem #1

Same problem as we did in class. Below is the mystery program. Its output is listed in the header of the program.

/* mystery.cpp
// D. T.
// mystery program
// To compile and run this program:
//
//     g++ mystery.cpp
//     ./a.out
//
// The output of the program is the following
//
// 2000000001
// -1294967294
//
// With what positive values were x and y initialized
// at the beginning of the program.  Explain why.
// An int contains 32 bits and is coded in 2's complement.
*/

#include <iostream>

using namespace std;

int main( int argc, char* argv[] ) {

    int x = ?????;
    int y = ?????;


    x = x+y;
    cout << x << endl;

    x = x+y;
    cout << x << endl;

    return 0;
}

What two positive numbers are stored in x and y to create the output listed in the header?

Explain your answer.

Problem #2

Assume that we want to compute the Fibonacci series with a compiled program written in a language that supports signed and unsigned ints, in 8-, 16-, 32-, and 64-bit length.

• How many terms can we correctly display if we use unsigned chars (8 bits) to store the Fibonacci terms?

• How many terms if we use unsigned short ints (16 bits)?

• How many terms if we use unsigned ints (32 bits)?

• How many terms if we use long unsigned ints of 64 bits?

• Repeat the same four questions for signed ints of 8, 16, 32, and 64-bit length.

Explain carefully how you derive your answers. Preferred answers are answers that contain a program (in the language of your choice) demonstrating/illustrating in one way or another the answers to the various questions.

Problem #3

class PowersOf2 {

    public static void main( String args[] ) {
        int x = 1;  

        while ( x != 0 ) { 
            System.out.println (  x ); 
            x = x * 2; 
        }
    }
}

• Why is the loop not an infinite loop?

• How many times does it go through? Why?

• What is the last number displayed by the loop? Why? Is it a valid power of 2?

• Assume now that we are interested in printing powers of 3, so we replace the multiplication line by "x = x * 3;" Is the loop infinite? Why or why not? If not infinite, what is the last number printed by the program?

Moodle Submission

• Submit your answers in 3 different files in the HW 6 PB 1, PB 2, and PB 3 sections on Moodle.