unsigned.cc

/*
 * This file contains code from "C++ Primer, Fifth Edition", by Stanley B.
 * Lippman, Josee Lajoie, and Barbara E. Moo, and is covered under the
 * copyright and warranty notices given in that book:
 * 
 * "Copyright (c) 2013 by Objectwrite, Inc., Josee Lajoie, and Barbara E. Moo."
 * 
 * 
 * "The authors and publisher have taken care in the preparation of this book,
 * but make no expressed or implied warranty of any kind and assume no
 * responsibility for errors or omissions. No liability is assumed for
 * incidental or consequential damages in connection with or arising out of the
 * use of the information or programs contained herein."
 * 
 * Permission is granted for this code to be used for educational purposes in
 * association with the book, given proper citation if and when posted or
 * reproduced.Any commercial use of this code requires the explicit written
 * permission of the publisher, Addison-Wesley Professional, a division of
 * Pearson Education, Inc. Send your request for permission, stating clearly
 * what code you would like to use, and in what specific way, to the following
 * address: 
 * 
 * 	Pearson Education, Inc.
 * 	Rights and Permissions Department
 * 	One Lake Street
 * 	Upper Saddle River, NJ  07458
 * 	Fax: (201) 236-3290
*/ 

#include <iostream>

int main()
{
	unsigned u = 10, u2 = 42;
	std::cout << u2 - u << std::endl;  
	std::cout << u - u2 << std::endl; 

	int i = 10, i2 = 42;
	std::cout << i2 - i << std::endl;
	std::cout << i - i2 << std::endl;

	u = 42;
	i = 10;
	std::cout << i - u << std::endl;
	std::cout << u - i << std::endl;

	u = 10;
	i = -42;
	std::cout << i + i << std::endl;  // prints -84
	std::cout << u + i << std::endl;  // if 32-bit ints, prints 4294967264

	i = 10;
	std::cout << "good" << std::endl;
	while (i >= 0) {
		std::cout << i << std::endl;
		--i;
	}

	for (int i = 10; i >= 0; --i)
		std::cout << i << std::endl;

	for (unsigned u = 0; u <= 10; ++u) 
		std::cout << u << std::endl;  // prints 0 . . . 10

/* NOTE: the condition in the following loop 
         will run indefinitely
	// WRONG: u can never be less than 0; the condition will always succeed
	for (unsigned u = 10; u >= 0; --u)
    	std::cout << u << std::endl;
*/
	u = 11; // start the loop one past the first element we want to print
	while (u > 0) {
		 --u;        // decrement first, so that the last iteration will print 0
		std::cout << u << std::endl;  
	}

	// be wary of comparing ints and unsigned
	u = 10;
	i = -42;
	if (i < u)               // false: i is converted to unsigned
		std::cout << i << std::endl;
	else
		std::cout << u << std::endl;   // prints 10

	u = 42; u2 = 10;
	std::cout << u - u2 << std::endl; // ok: result is 32
	std::cout << u2 - u << std::endl; // ok: but the result will wrap around
}