Header Files and User Code

In math.h we have declarations

      extern double sqrt (double);
      extern double sin (double);
      extern double cos (double);
      /* and many more declarations ... */

In user.c we have definition of user code

      #include <math.h>

      double x, y, z, r;
      /* initialization, etc. */
      r = sqrt (x*x + y*y + z*z);

• use the same header file in user code

• user code then compiles correctly with implicit conversions as needed