CODEWITHSUNDEEP
cfloating-pointfloating-point-conversion
Harman
Harman

Reputation: 1581

Comparing Float Values in C

I want to compare float values to determine the biggest number in the list.The precision of the float is fixed, 6 after the decimal.

Should I just compare them as integer and if they are equal then go and dig the values after the decimal ?

Upvotes: 0

Views: 6841

Answers (6)

pekon
pekon

Reputation: 31

Following article provides various alternatives on comparing float values.. http://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/

Usually, finding the difference between the floats and checking if the difference is within the precision limit, helps in comparing the floats. But as also mentioned, there is no perfect answer and implementation for this because different between adjacent floats varies with the magnitude. Hence if you know the range of values which your program will use, then you can chose appropriate implementation for comparison.

Upvotes: 0

EvilTeach
EvilTeach

Reputation: 28882

use DBL_EPSILON as a basis for how close to doubles need to be.

use FLT_EPSILON exists for floats.

see this answer for a sample function that demonstrates the technique.

Upvotes: 1

David Heffernan
David Heffernan

Reputation: 613572

Code to do this looks like the following:

float MinFloatArray(float *a, int n)
{
    int i;
    float result = MAX_FLOAT;
    for (i=0; i<n; i++)
        if (a[i]<result)
            result = a[i];
    return result;
}

Upvotes: 0

glglgl
glglgl

Reputation: 91149

That depends on things you don't tell us.

  • How are these numbers provided to you? As strings, or are they already in the memory (float array/double array)?
  • How large are they? Is there any greatest boundary, in order to have a certain precision? I.e., are the 6 decimals relevant if the number is, let's say, 100 millions?
  • Is it ok to lose precision?

etc.

As you have the values in a float array, I would do the following:

float biggest(float * values, int num)
{
    int i;
    float curmax;
    if (num == 0) return NAN;
    curmax = values[0];
    for (i=1; i < num; i++) {
        if (values[i] > curmax) curmax = values[i];
    }
    return curmax;
}

Upvotes: 0

Dave
Dave

Reputation: 11162

The easiest way to compare floats is with the < operator, like so

if(float1 < float2)
     printf("%f < %f\n", float1, float2);

Upvotes: 2

Kusalananda
Kusalananda

Reputation: 15633

If you want to find the biggest number, why would you need to worry about comparing for equality?

Upvotes: 0

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