Geek Answers Handbook

For a loop in C ++, using a double break one step earlier, the limit value is not reached

I have a simple C ++ program compiled using gcc 4.2.4 on 32-bit Ubuntu 8.04. It has for-loop, in which the variable is doubleincremented from zero by one with a certain step size. When stride size 0.1, behavior is what I expected. But when the step size is "0.05", the loop exits after 0.95. Can someone tell me why this is happening? The result follows the source code below.

#include <iostream>

using namespace std;

int main()
{
    double rangeMin = 0.0;
    double rangeMax = 1.0;
    double stepSize = 0.1;

    for (double index = rangeMin; index <= rangeMax; index+= stepSize)
    {
        cout << index << endl;
    }
    cout << endl; 

    stepSize = 0.05;
    for (double index = rangeMin; index <= rangeMax; index+= stepSize)
    {
        cout << index << endl;
    }

    return 0;
}

EXIT

sarva@savija-dev:~/code/scratch$ ./a.out 
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1

0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
sarva@savija-dev:~/code/scratch$
+5
source share
10 answers

, 0.95+0.05 > 1, 0.95 double.

, Wikipedia .

IEEE, , 0.95 64- (double) 0-01111111110-1110011001100110011001100110011001100110011001100110, , 0.95000016 0.05 1.0.

(, , ).

+16

, , , " ". :

if ( fabs(double1-double2) < 0.0000001 ) {
  do-something
}

- .

+11

== <= - . 0.95000000000000029. :

stepSize = 0.05;
// stepSize/2 looks like a good delta for most cases
for (double index = rangeMin; index < rangeMax+stepSize/2; index+= stepSize)
{
    cout << index << endl;
}

.

+6

, - . IEEE .

+6

.

Goldberg .

+4

, index 1.00000001.

+2

, , "" . , : 1/3 (0,33), (1/3) * 3 0.99, 1.

- "", .

,

stepSize = 0.05;
for (double index = rangeMin; index <= rangeMax; index+= stepSize)
{
    cout << index << endl;
}

-

stepSize = 0.05;
for (int index = 0; index < 21; ++index)
{
    double value = rangeMin + index * stepSize;
    cout << value << endl;
}
+2

. 0,1 0,05, , . .

, .

+1

. : ( )

#include <iostream>
#include <iomanip>
using namespace std;
int main(){
    double rangeMin = 0.0;
    double rangeMax = 1.0;
    double stepSize = 0.1;
    double index;
    for (index = rangeMin;  index <= rangeMax; index+=stepSize)
        {
               cout << fixed << setprecision(16) <<  index << endl;
         }
  cout << endl;
  stepSize = 0.05;
  for (index = rangeMin; index<= rangeMax; index+= stepSize)
     {
         cout << index << endl;
             }

   cout << "\n" << setprecision(16) << index << " "  << rangeMax;
   if(index==rangeMax)
      cout << "\nEQ";
   else
     cout << "\nNot EQ";
     return 0;
}

0.0000000000000000
0.1000000000000000
0.2000000000000000
0.3000000000000000
0.4000000000000000
0.5000000000000000
0.6000000000000000
0.7000000000000000
0.7999999999999999
0.8999999999999999
0.9999999999999999

0.0000000000000000
0.0500000000000000
0.1000000000000000
0.1500000000000000
0.2000000000000000
0.2500000000000000
0.3000000000000000
0.3500000000000000
0.4000000000000000
0.4500000000000000
0.4999999999999999
0.5499999999999999
0.6000000000000000
0.6500000000000000
0.7000000000000001
0.7500000000000001
0.8000000000000002
0.8500000000000002
0.9000000000000002
0.9500000000000003

1.0000000000000002 1.0000000000000000
Not EQ
+1

, for-loops. , , , :

#include<iostream>
#include<cmath>
#include<iomanip>
using namespace std; 

int main()
{
for (double y = 1; y!=10; y += 1)
    cout << static_cast<double>(y/10) << endl; 



}
+1

More articles:


All Articles