float

[mickey]

Do anyone have an idea of this behaviour???

cout << Density << "\n"; //this print 0.13
float f = Density*100;
slider1->setValue(f); //this set slider1 to 12!!!! why????

cout << Density << "\n"; //this print 0.13
float f = Density*100;
slider1->setValue(f); //this set slider1 to 12!!!! why????

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float f = 0.13*100;
slider1->setValue(f);  //this set slider1 to 13

float f = 0.13*100;
slider1->setValue(f);  //this set slider1 to 13

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[wysota]

Probably due to limited precision of float and implicit floor casting to int.

Did you ever try to compare float values ?
Check this out:

#include <iostream>
 
int main(){
  float n = 0.99;
  while(n!=0.09){
    std::cout << n << std::endl;
    n-=0.01;
  }
  return 0;
}

#include <iostream>

int main(){
  float n = 0.99;
  while(n!=0.09){
    std::cout << n << std::endl;
    n-=0.01;
  }
  return 0;
}

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Try this to make your app work:

float f = Density*100;
slider1->setValue((int)(0.5+f));

float f = Density*100;
slider1->setValue((int)(0.5+f));

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The second line is equivalent to

slider1->setValue(round(f));

slider1->setValue(round(f));

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but Windows doesn't know how to round(), so a hack like (int)(0.5+f) is needed.

[Zatraz]

Because in the fallow code line:

float f = Density*100;

float f = Density*100;

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and

float f = 0.13*100;

float f = 0.13*100;

To copy to clipboard, switch view to plain text mode 

the number "100" in implicity cast to a float and this conversion could lead to a precision lost.

Try to use:

float f = Density*100.0;

float f = Density*100.0;

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and

float f = 0.13*100.0;

float f = 0.13*100.0;

To copy to clipboard, switch view to plain text mode 

[mickey]

Because in the fallow code line:

float f = Density*100;

float f = Density*100;

To copy to clipboard, switch view to plain text mode 

and

float f = 0.13*100;

float f = 0.13*100;

To copy to clipboard, switch view to plain text mode 

the number "100" in implicity cast to a float and this conversion could lead to a precision lost.

Try to use:

float f = Density*100.0;

float f = Density*100.0;

To copy to clipboard, switch view to plain text mode 

and

float f = 0.13*100.0;

float f = 0.13*100.0;

To copy to clipboard, switch view to plain text mode 

sorry but your example doesn't solve the problem......

[wysota]

Try mine, it should work just fine.

[mickey]

Try mine, it should work just fine.

yes I just use it! I thanked you for this......