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   assert

   Usage
   #include <assert.h>
   void assert(expression);

   Description
   The  assert macro is useful for adding internal consistency checks  to
   programs.  When the assert macro is executed it checks the  expression
   argument  and if it is zero, then the following message is printed  on
   the standard error device and the program aborts.
   Assertion failure: 'expression' on line ?? in file '???'
   The  assert function can be deactivated by defining the  macro  NDEBUG
   prior to the inclusion of assert.h header file. This has the effect of
   turning all assertions into null statements.

   Example
   #include <assert.h>
   #include <stdio.h>
   char *string = "";
   /* empty string */
   int value = 1;
   main()
   {
        assert(value > 0);
        printf("Passed assert(value > 0)\n");
        assert(*string != '\0');
   }