[: More must be said here about the complex functions' ranges.]

#include <math.h>
float sinf(float a);
double sin(double a);
long double sinl(long double a);

#include <complex.h>
float complex csinf(float complex a);
double complex csin(double complex a);
long double complex csinl(long double complex a);

#include <tgmath.h>
floating-type sin(floating-type a);

The sin functions take an angle a in radians, and return the sine of that angle, sin a.

#include <math.h>
float asinf(float r);
double asin(double r);
long double asinl(long double r);

#include <complex.h>
float complex casinf(float complex r);
double complex casin(double complex r);
long double complex casinl(long double complex r);

#include <tgmath.h>
floating-type asin(floating-type r);

The asin functions take a ratio r and return the arc sine of that ratio, sin⁻¹ r, in the range [−½π, +½π].