floating point comparison

[cag27]

Just a quick question--is there a way to do an accurate comparison of floating point numbers? Here's an excerpt of the code that I'm working on:

//this while loop will be executed if the user
//enters a negative or zero value as a check
//amount
while( *ptr < 0.01)
{
printf(&quot;Please enter a positive amount for the check: &quot;
scanf(&quot;%f&quot;, ptr);
getchar();
} //end of while loop

Unfortunately, when '0.01' is entered, I go into the while loop. I know that 1/100 cannot be accurately represented in binary and that this must be what is causing the problem, but does anyone have any a relatively simple way to solve this problem? Thank you.

Carrie

 

[Zyrenthian]

have your tried something along the lines of...

char myValue[MAX_SIZE];

sprintf(myValue,&quot;%f&quot;,*ptr);

and then

while(strcmp(myValue,&quot;0.01&quot<0) // string 1 less

On a side note, make sure the sprintf writes it as 0.01 and not as .01 or you will run into problems.


matt

 

[smaniraja]

Yes you are right cag27, problems are there in processing the floating numbers, but you can solve this by using double precession numbers.

But in this case its different. I think the ptr is an floating point variable [ your are using %f to read it ], but while checking you used the expression (*prt < 0.01). Here you are checking a floating point number with a double number [ 0.01 is a double precession number by default, if you want to represent it as a float number then you have put 0.01f ]. While accessing a float 0.01 [0.01f] this will something less 0.01, but while using double 0.01 [ 0.01 ] this is 0.01 only.

So make this expression like (*ptr < 0.01f) this. Otherwise declare the ptr as a double variable and use the expression as it is [ while reading the double number put %g ]. These two expressions will check prefectly.

Regards
Maniraja S

 

[cag27]

Zyrenthian and smaniraja,
Thank you both for your suggestions--I went with the second option of just adding the 'f' to 0.01 in my while comparison, and it works great! I knew that there had to be some simple way to fix the problem, and there was! Thanks again.

Carrie