Why an expression instead of a constant, in a C for-loop's conditional?

Why an expression instead of a constant, in a C for-loop's conditional?

c for-loop coding-style expression constantfolding

c

log(10.0) can compile but log(0.0) cannot with undefined reference?

c gcc math.h constantfolding

c

Why does GCC implement isnan() more efficiently for C++ <cmath> than C <math.h>?

c++ c optimization nan constantfolding

c