### _fpatan -- Calculate Arctangent

Format

>     #include <builtin.h>
>     double _fpatan(double x);

Language Level: Extension
_fpatan calculates the arctangent of x, which is a value in radians between -PI/2 and PI/2. This function causes the compiler to emit the appropriate 80387 instruction for the calculation of arctangent.

Because it is a built-in function and has no backing code in the library:

- You cannot take the address of _fpatan.
- You cannot parenthesize a _fpatan function call, because parentheses specify a call to the backing code for the function.

Return Value
This function returns the arctangent of x.

Example
This example calculates the arctangent of x.

    #include <builtin.h>
    #include <stdio.h>

    int main(void)
    {
       double x;

       x = 0.45;
       printf("The arctangent of %lf is %lf.\n", x, _fpatan(x));
       return 0;

       /********************************************************
          The output should be :

          The arctangent of 0.450000 is 0.422854.
       ********************************************************/
    }

atan - atan2 -- Calculate Arctangent
_fptan -- Calculate Tangent
tan -- Calculate Tangent
tanh -- Calculate Hyperbolic Tangent
<builtin.h>