Evaluating relational operator in C

Question

Given below is a segment of code in C

float k=0.6;

if(k==0.6)
  printf("yes they are equal");
else
  printf("no they are not equal");

The above code gives output "no they are not equal". I am working on Ubuntu 12.04 gcc 4.4

I was surprised and debugged the program. The answer is no because the value of K is not equal to 0.6. I single stepped the program in gdb and i found value of k as 0.600000024. Now my question is why 0.600000024 is assigned to k and why not 0.6. when I assign 0.7 the k has a value 0.69999998. Why does this happen?

The answer is no because the value of K is not equal to 0.6. I single stepped the program in gdb and i found value of k as 0.600000024 — user146297, Apr 08 '15 at 06:05
The type of `0.6` is not `float`, it's `double`. There's a duplicate somewhere. — Yu Hao, Apr 08 '15 at 14:01

score 0 · Answer 1 · answered Apr 08 '15 at 13:55

0

Correct. If you are working with float values in C you have to work with a set difference.

You can use

DBL_EPSILON of the Header float.h
if ((k - 0.6) < DBL_EPSILON){ ... }

answered Apr 08 '15 at 13:55

Andréw

96
1
11

Thank you. I will read up more on floating points – user146297 Apr 09 '15 at 13:45

Evaluating relational operator in C

1 Answers1