#include <math.h>
double log10(double x);
log10 computes the base-10 logarithm of x.
If x = 0, errno is set to ERANGE
and log10 returns -HUGE_VAL.
If x < 0, errno is set to EDOM
and log10 returns -HUGE_VAL.
If x < 0 or x = -?, log10 returns
NaN with signal.
If x = 0, log10 returns -? with signal.
If x = ?, log10 returns ?.
If x = NaN, log10 returns x
with no signal.
log10 conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).