Digits Counter after decimal points

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hmmm in last loop when it assigns the value of int (b) to d...it always assigns int (b)-1 value to it...like if i enter 10.37 then the values on output are like given below...
http://postimg.org/image/4hetuo873/[^]

C++

// Decimal Points Couter.cpp : Defines the entry point for the console application.
    //
     
    #include "stdafx.h"
    #include <iostream>
    #include <conio.h>
    using namespace std;
    int main ()
    {
            double a,b,c,d;
            int i=0;
            cout << "Enter number a:";
            cin >> a;
            b=a-int (a);
            cout << '\n';
            cout << b << endl;
            cout << '\n' << '\n';
        loop:
            b=b*10;
            cout << b << endl;
        d=int (b);
            cout << d << endl;
            c=b-d;
        cout << c << endl;
            b=c;
            i++;
            cout << '\n';
            if (b>0) goto loop;
        cout << i ;
            _getch();
            return 0;
    }

Posted 28-Jun-13 1:06am

ImpedanceZ

Updated 28-Jun-13 2:22am

nv3

v5

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Comments

Maciej Los 28-Jun-13 7:12am

What's the question?

ImpedanceZ 28-Jun-13 7:23am

hmmm in last loop when it assigns the value of int (b) to d...it always assigns int (b)-1 value to it...like if i enter 10.37 then the values on output are like given below...
http://postimg.org/image/4hetuo873/

Richard MacCutchan 28-Jun-13 8:34am

Instead of pointing to an external link try explaining your problem properly. What results do you get and what should you get, would be a start.

ImpedanceZ 28-Jun-13 8:42am

hmmm ok...I get value to of d=int (b)-1...and I need value of d=int (b) to make c=0 and to terminate the loop...
Actually in last loop the value of float b is integer value itself like 1,2,3,etc...

Richard MacCutchan 28-Jun-13 8:59am

Ah, that makes it so much clearer.

3 solutions

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

nv3 · Accepted Answer · 2013-06-28T02:34:00

Solution 1

When you multiply a fraction like 0.7 by 10.0 you receive a result that is close to 7.0 but not exactly 7.0. The result might for example be 6.999998. And if you assign that to an int variable the result will be 6.

The reason for that behavior is that in double variables fractions are stored in the binary system, not in the decimal system. For example 0.7 has no exact representation as a binary fraction. And that is why instead of 0.7 the double variable holds something like 0.699999999999.

Posted 28-Jun-13 2:34am

nv3

Comments

ImpedanceZ 28-Jun-13 8:46am

so how can I actually count the value of digits after decimal points?

nv3 28-Jun-13 9:46am

Strictly speaking, trying to count the digits in the fractional part does not make much sense. In the case of 0.6999999999999 you would get 12. What you expected was 1 - corresponding 0.7.

What you can do: Make an assumption about the accuracy of the value in your double variable, for example 10**-6. Then compare the remainder of the fraction in your loop to that accuracy and abort the loop if the remainder is either in the range of 1.0 +/ epsilon or 0.0 +/- epsilon (epsilon being the assumed accuracy).

ImpedanceZ 28-Jun-13 10:00am

thanx bro :) didn't get about assumption of accuracy because I have just started learning c++.
anyways thanx :) I found another way to find number of digits :)

CPallini · Accepted Answer · 2013-06-28T02:39:00

I'm not sure I got you, however it seems related on the classic problem people have with double numbers. Computer-stored double numbers are not (maths) real numbers: they are memory constrained and cannot achieve inifinite precision (see for instance "Double-precision floating-point format" at Wikipedia[^]). In your case, if you see (for instance with the debugger) the actual number in computer memory representing 10.37 then you could be surprised by the 'strange' 10.369999999999999.

ImpedanceZ · Accepted Answer · 2013-06-28T03:24:00

This is what i got ...thanx for your support :)

C++

#include "stdafx.h"
   #include <iostream>
   #include <conio.h>
   using namespace std;
   int main ()
   {
           double a,b;
           int i=0;
           cout << "Enter number a:";
           cin >> a;
           cout << '\n';
           do
           {
           a=a*10;
           cout << a << endl;
           b=a-int (a);
           cout << b << endl;
           i++;
           cout << '\n';
           }while (b!=0);
           cout << i << endl;
            _getch();
           return 0;
   }

Digits Counter after decimal points

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Digits Counter after decimal points

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