Programming in C

Math Functions 483

int islessequal (x, y)

Is x≤ y?

int islessgreater (x, y)

Is x< yor is x> y?

int isnan (x)

Is xa NaN (that is, not a number)?

int isnormal (x)

Is xa normal value?

int isunordered (x, y)

Are xand yunordered (for example, one or both might be NaNs)?

int signbit (x)

Is the sign of xnegative?

In the list of functions that follows,x,y,and zare of type double,ris an angle expressed

in radians and is of type double,and nis an int.

For more information about how errors are reported by these functions, consult your

documentation.

double acos (x)^1

Returns the arccosine of x,as an angle expressed in radians in the range [0,π].xis in

the range [–1, 1].

double acosh (x)

Returns the hyperbolic arccosine of x,x ≥ 1.

double asin (x)

Returns the arcsine of xas an angle expressed in radians in the range [–π/2,π/2].

xis in the range [–1, 1].

double asinh (x)

Returns the hyperbolic arcsine of x.

1.The math library contains float, double, and long double versions of the math functions that take

and return float, double, and long double values.The double versions are summarized here.The

float versions have the same name with an fon the end (e.g.acosf).The long double versions

have an lon the end instead (e.g.acosl).

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