Re: 0 isn't 0 in C++ math
Quote:
Originally Posted by
justutiz
OK, i have a script, which calculate ...
Scripts are not discussed in this Forum.
There is a Visual C++ Programming forum, and Visual C++ is code, not script.
Quote:
Originally Posted by
justutiz
... which calculate Y=1/(C-A). C is input, A is intetrval [Ap;Ag] with step Az;
Did you, perhaps, mean "A is a value within intetrval [Ap;Ag]"?
Anyway, have a look at:
Floating point
What Every Computer Scientist Should Know About Floating-Point Arithmetic
and a lot of other articles/discussions here
Re: 0 isn't 0 in C++ math
Quote:
Originally Posted by
VictorN
Im reading, and Im very new in C++, so I dont find how I can do the folowing that a == c, then a and c is floats.
Re: 0 isn't 0 in C++ math
Quote:
Originally Posted by
justutiz
... so I dont find how I can do the folowing that a == c, then a and c is floats.
In general you cannot just compare floats as "a == c". You have to implement some relative small (with respect to the "a" and "c") value ("delta") and compare like:
Code:
if(abs(a - c) < delta)
{
...
}
Re: 0 isn't 0 in C++ math
but abs want me to use int, my a and c is floats
Re: 0 isn't 0 in C++ math
Well, I meant this abs, _abs64
However, you can use fabs instead.
Re: 0 isn't 0 in C++ math
Quote:
when i want to say that 0 isn't possible in 1/0, the program colculate me: Y = -2.1e+06
Result of 1/0 is infinity, while programming languages operate with only finite figures. So you have the best result FPU was able to provide. :)
Re: 0 isn't 0 in C++ math
Im still geting
Code:
1 -1 0
1.11 -0.9 0
1.25 -0.8 0
1.43 -0.7 0
1.67 -0.6 0
2 -0.5 0
2.5 -0.4 0
3.33 -0.3 0
5 -0.2 0
10 -0.1 0
-1.34e+07 7.45e-08 0
-10 0.1 0
-5 0.2 0
-3.33 0.3 0
-2.5 0.4 0
-2 0.5 0
-1.67 0.6 0
-1.43 0.7 0
-1.25 0.8 0
-1.11 0.9 0
trying everything, and still dont get how to fix it.
Code:
#include <iostream>
#include <cstdlib>
#include <iomanip>
#include <math.h>
using namespace std;
int main ()
{
float y, c, ap, ag;
c = 0;
ap = -1;
ag = 1;
float az = 0.1;
if (ag > ap && az > 0.0) {
for (float a = ap; a <= ag; a += az) {
if ( fabsf(c - a) < 0.0 && fabsf(c - a) > 0.0 ) {
cout << "1/0 not posible";
}
else {
y = 1.0 / (c - a);
cout << setprecision(4) << y <<" " << a << " " << c << endl;
}
}
}
else cout << "STOP";
system ("pause");
return 0;
}
Re: 0 isn't 0 in C++ math
It's impossible to succeed with the condition fabsf(c - a) < 0.0. Victor meant something like fabsf(c - a) < 0.00001.
Re: 0 isn't 0 in C++ math
Quote:
Originally Posted by
Igor Vartanov
Result of 1/0 is infinity, while programming languages operate with only finite figures. So you have the best result FPU was able to provide. :)
Yes, but why in my code -0.1 + 0.1 is not 0?
Re: 0 isn't 0 in C++ math
Quote:
Originally Posted by
Igor Vartanov
It's impossible to succeed with the condition fabsf(c - a) < 0.0. Victor meant something like fabsf(c - a) < 0.00001.
Yes, it works, but maybe it is shortes way to compare c-a is 0?
Re: 0 isn't 0 in C++ math
Quote:
Originally Posted by
justutiz
Yes, but why in my code -0.1 + 0.1 is not 0?
I don't know what's wrong with your code, but mine works fine:
Code:
#include <stdio.h>
int main()
{
float a = -0.1;
printf("%f", a +0.1);
return 0;
}
Quote:
D:\Temp\8>8.exe
-0.000000
Re: 0 isn't 0 in C++ math
Quote:
Originally Posted by
Igor Vartanov
I don't know what's wrong with your code, but mine works fine:
Code:
#include <stdio.h>
int main()
{
float a = -0.1;
printf("%f", a +0.1);
return 0;
}
when add one time its true, but when you do it with cycle it looks something like this
a = -0.1 + 0.01000000001 and so on
and then you compare 0 with a it is looks something like this 0 != 0.0000000000001
Re: 0 isn't 0 in C++ math
Quote:
Originally Posted by
justutiz
Yes, it works, but maybe it is shortes way to compare c-a is 0?
Well, the big mistake you make is that you think math and programming are the same. Floats in programming have finite precision, so you must take certain precautions and tricks to succeed with your calculations. Like comparing with 0.00001, for example.
Re: 0 isn't 0 in C++ math
Quote:
Originally Posted by
justutiz
when add one time its true, but when you do it with cycle it looks something like this
a = -0.1 + 0.01000000001 and so on
and then you compare 0 with a it is looks something like this 0 != 0.0000000000001
Yep, see above: float calculations have finite precision. And the result might fluctuate a little. :)