text: //<math.h>
  //example shows the usage of atan() function.
  
  #include <stdio.h>
  #include <math.h>
  
  #define PI 3.14159265
  
  int main () {
     double x, ret, val;
     x = 1.0;
     val = 180.0 / PI;
  
     ret = atan (x) * val;
     printf("The arc tangent of %lf is %lf degrees", x, ret);
  
     return(0);
  }
  