Negetive Numbers

This is a discussion on Negetive Numbers within the C++ Programming forums, part of the General Programming Boards category; I wrote this program, and when it generates 50 or so numbers, it starts making them negative. Any ideas why? ...

  1. #1
    using namespace Trooper; St0rmTroop3er's Avatar
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    Negetive Numbers

    I wrote this program, and when it generates 50 or so numbers, it starts making them negative. Any ideas why?

    Code:
    #include <iostream>
    
    using namespace std;
    
    int fibonacci(int n);
    
    int main()
    {
    	cout << "Ryan's Fibonacci Number calculator.\n";
    	int input;
    	while(input != 0)
    	{
    		if(input == 0) break;
    		
    		cout << "Enter how many Fibonacci Numbers to calculate.\nEnter 0 to quit: ";
    		cin >> input;
    		fibonacci(input);
    	}
    }
    
    int fibonacci(int n)
    {
    	int first = 0;
    	int second = 1;
    	while(n--)
    	{	
    		cout << first << "\n";
    		int tmp = first+second;
    		first = second;
    		second = tmp;
    	}
    }

  2. #2
    Slave MadCow257's Avatar
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    You're exceeding the range of an int, so it wraps. To help that, you could set a max number, make it unsigned, and/or increase to an int64

  3. #3
    Frequently Quite Prolix dwks's Avatar
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    Eventually even an int64 would run out. You can implement your own infinite-digit number class or you could use something like GMP.
    dwk

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  4. #4
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    Quote Originally Posted by dwks
    Eventually even an int64 would run out. You can implement your own infinite-digit number class or you could use something like GMP.
    It is not possible to implement an infinite-digit number class, because you are always constrained by the amount of addressable memory available to your program. So any value you can represent is always finite (albeit able to hold pretty large values).

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    Last edited by Decrypt; 03-14-2006 at 08:29 AM. Reason: added link
    There is a difference between tedious and difficult.

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