Division by zero

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I had a function:

double Normalize(double v, double c)
{
    return 1.0 / (1.0 - (v * v) / (c * c)); 
}

It worked correctly until I called it with zero argument by mistake:

double x = Normalize(2, 0);
Console.WriteLine(x);

It outputs 0, no exception. How come?! Everyone learned divide by zero is impossible. How can I be sure calculation is correct if there is division by zero in the middle?

Posted 4-Jan-11 12:36pm

programmer095

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Roger Wright · Answer 1 · 2011-01-04T19:59:00

When you passed the function (2,0) as arguments, you handed it int values and asked it to implicitly cast them to type double. The results are indeterminate, and there may be dangling non-zero bits in the LSB of the result. Squaring that value and dividing by it can produce any result, including 0 and infinity. If you pass the function (2.0, 0.0), which are explicit floating point values, I think you'll get the exception you're expecting.

luisnike19 · Answer 2 · 2011-01-04T12:56:00

Solution 2

Yo could separate the operations and then check if the division is Infinite

if(double.IsInfinity(down))
{
  //Exception
}

or validate this case, if your "c" is 0, then exception

Posted 4-Jan-11 12:56pm

luisnike19

Comments

programmer095 4-Jan-11 19:07pm

Who will need to check infinity after every division?! With C++ there was exception -- all I need

Dalek Dave 5-Jan-11 5:13am

That is what I would do, simple one-line check.

JF2015 5-Jan-11 5:19am

Good one!

Not Active · Answer 3 · 2011-01-04T12:53:00

Solution 1

If you step through this code you will see (c * c), where c = 0, is -Infinity, not zero since you are using a floating-point type, double, as the data type. Change it int and it will throw the exception you expect.

http://msdn.microsoft.com/en-us/library/678hzkk9(v=VS.100).aspx[^]

Posted 4-Jan-11 12:53pm

Not Active

Updated 4-Jan-11 12:54pm

v2

Comments

programmer095 4-Jan-11 19:08pm

I see, thank you. My variable in real not int, it is double

Amarkhel · Answer 4 · 2011-01-04T23:11:00

We need to assign one if clause to spacify the condiction that if a user assign zero show the maassage like:

initialize the variable in public and write:

double x;
double y;
double z;
string op;

under oparent button we write:

x=system.convert.tostring(texbox?.text);
op=/;
if(y=0)
{
massagebox.show("can't be devided");
}

Safiullah
Afghanistan

Division by zero

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