GCC gives incorrect answer with optimization enabled

Question

I have the following C program

double d = 1.4;
int x;
x = d * 10;
printf("\n\n VALUE = %d " ,x);

I have gcc 4.3.3 which comes with Ubuntu 9.04

I get answer as 13 with -O0 but get correct answer i.e 14 with higher levels of optimization

Is this a known issue or something wrong with my code?

Answer 1

You can't represent 1.4 exactly using double, the value is actually a bit lagrer or a bit smaller (see this). So there is no "correct" answer - use round() instead of implictly truncating.

Answer 2

This is gcc bug #323 , in reality this is not a bug but an implementation detail.