#include <math.h>

double asin (
  double x);   /* number to calculate arc sine of */

The asin function calculates the arc sine of the floating-point number x.

The asin function returns the arc sine of x.

For x ∈ [-1, 1], asin(x) → [-π/2, π/2].
For x ∈ (-∞, -1) ∪ (1, ∞), asin(x) → NaN.

acos, atan, atan2

#include <math.h>
#include <stdio.h> /* for printf */

void tst_asin (void) {
  float x;
  float y;

  for (x = -1.0; x <= 1.0; x += 0.1) {
    y = asin (x);
    printf ("ASIN(%f) = %f\n", x, y);
  }
}