Header Files and Definitions

In math.h we have declarations

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

In math.c we have definitions

      #include <math.h>

      double sqrt (double)
      { /* compute result */
        return result;
      }

      double sin (double)
      { /* compute result */
        return result;
      }

      /* more definitions ... */

• #include includes the contents of the named file

• declaration in header files is used in compilation of the library function

• any mismatch between declaration and definition is flagged as warning

• so check compiler warnings