/*
 * hodge-podge of mathematical functions
 *
 * Matt Bishop
 * -- May 22, 2024	original program
 */
#include <stdio.h>
#include <math.h>
#include <string.h>
#include <errno.h>

/*
 * a useful constant
 */
#define PI	3.141592653

/*
 * prototypes
 * this is supposed to be defined in math.h but it isn't
 */
int isnan(double);	/* true if argument is not a valid float or double */

/*
 * start here
 */
int main(void)
{
	double x, y;	/* used to hold various values */

	/* first get the floor and ceiling of a double */
	printf("\nGet the floor and ceiling of 7.28:\n");
	printf("ceil(7.28) = %f\n", ceil(7.28));
	printf("floor(7.28) = %f\n", floor(7.28));

	/* now floating point absolute value */
	printf("\nGet the absolute value of 3.14 and then -3.14:\n");
	printf("fabs(3.14) = %f\n", fabs(3.14));
	printf("fabs(-3.14) = %f\n", fabs(-3.14));

	/* now log base 10 and exponentiation */
	printf("\nGet the log base 10 of 34.6, and raise 10 back to that power:\n");
	x = log10(34.6);
	y = pow(10, x);
	printf("log10(34) = %f -- pow(10, %f)\n", x, y);
	printf("but don't compare floats or doubles: pow(10, log10(34.6)) %s 34.6\n", y == 34.6 ? "==" : "!=");

	/* remainder for doubles */
	printf("\nGet the remainder of 8.2 when divided by 4.1 and 4:\n");
	printf("fmod(8.2, 4.1) = %f\n", fmod(8.2, 4.1));
	printf("fmod(8.2, 4) = %f\n", fmod(8.2, 4));

	/* get fraction, integer parts of a double */
	printf("\nGet the integer and fraction parts of 8.21349:\n");
	x = modf(8.2, &y);
	printf("modf(8.2, &y) = %f, so the integer part is %f and the fraction part is %f (or %d)\n", x, x, y, (int) y);

	/* take the square root of 123.456 */
	printf("\nGet the square root of 123.456:\n");
	printf("sqrt(123.456) = %f\n", sqrt(123.456));

	/* now some trig */
	printf("\nGet the sine of pi/6 = %f, and then invert it to get pi:\n", PI / 6);
	x = sin(PI/6);
	y = asin(x);
	printf("sin(pi/6) = %f; asin(%f) = %f; and 6*asin(%f) = %f\n", x, x, y, y, 6 * y);

	printf("\nGet the cosine of pi/6 = %f, and then invert it to get pi:\n", PI / 6);
	x = cos(PI/6);
	y = acos(x);
	printf("cos(pi/6) = %f; acos(%f) = %f; and 6*acos(%f) = %f\n", x, x, y, y, 6 * y);

	printf("\nGet the tangent of pi/6 = %f, and then invert it to get pi:\n", PI / 6);
	x = tan(PI/6);
	y = atan(x);
	printf("tan(pi/6) = %f; atan(%f) = %f; and 6*atan(%f) = %f\n", x, x, y, y, 6 * y);

	/* finally, show what happens when you get something that's not a number */
	printf("\nNow we show something that is not a number, namely the square root of -1:\n");
	errno = 0;		/* make sure it is cleared */
	x = sqrt(-1.0);
	printf("sqrt(-1) = %f", x);
	if (isnan(x))
		printf(" -- and here is the system error: '%s'\n", strerror(errno));

	/* all done! */
	return(0);
}