{{keywords>wiki library source code example reference}}
===== atan =====

<code c>
    double atan(double);
</code>

calculates acustangens from a number

===== C Sourcecode Example =====

compile in linux with: gcc atan.c -o atan **-lm** -Wall
<code c>
#include <stdio.h> /* including standard library */
//#include <windows.h> /* uncomment this for Windows */

#include <math.h> /* including math library */

int main ( void ){
    double a=0.2;
    printf("atan from %f is %f\n", a, atan(a) * 90 / 3.17);
    return 0;
}
</code>    
===== output =====
    
    output:
    user@host:~$ ./atan 
    atan from 1.200000 is 24.872311