Regarding floats and comparison operator in C

Question

int main()
{
    float lfResult = 19.893196;
    if(lfResult == 19.893196)
        printf("Works");
    else
        printf("does not work");

    getch();
    return 0;
}

Output: does not work

Why does the if condition fail?

You might like this blog post: http://blog.frama-c.com/index.php?post/2011/11/08/Floating-point-quiz — Pascal Cuoq, Aug 08 '12 at 15:22
exact duplicate of http://stackoverflow.com/questions/1839422/strange-output-in-comparision-of-float-with-float-literal — tinman, Aug 08 '12 at 16:55

score 8 · Answer 1 · answered Aug 08 '12 at 07:12

In C floating constants have the type double. Try:

float lfResult = 19.893196f;
if(lfResult == 19.893196f)
                        ^

Thus the constant 19.893196 has more precision than lfResult.

6.4.4.2 - 4

An unsufﬁxed ﬂoating constant has type double. If sufﬁxed by the letter f or F, it has type float. If sufﬁxed by the letter l or L, it has type long double.

score 1 · Answer 2 · answered Aug 08 '12 at 07:14

1

your literal is a double, casted to float in assignement.

try:

if(lfResult == 19.893196F)
  ...

answered Aug 08 '12 at 07:14

CapelliC

59,646
5
47
90

score 0 · Answer 3 · answered Aug 08 '12 at 07:19

0

In if condition, 19.893196 can be taken as double. So the if condition fails.

You should try like following way.

if(lfResult == 19.893196f)

I think it will be helpful to you.

answered Aug 08 '12 at 07:19

Prasad G

6,702
7
42
65

Regarding floats and comparison operator in C

3 Answers3