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>From steve Fri Nov 24 21:46:23 1989
Subject: C code
To: evan@telly (Evan Leibovitch)
Date: Fri, 24 Nov 89 21:46:23 EST
From: Steve Bird <steve@cohort.UUCP>
X-Mailer: ELM [version 2.2 PL7]

 Here's another interesting piece. 

     /* floaterr.c--demonstrates round-off error */
     # include <stdio.h>
     main()
       {
         float a,b;
         b = 2.0e20 + 1.0;
         a = b - 2.0e20;
         printf("%f \n",a);
       }

  When compiled the program returns the number 4008175468544.000000 .
  Now when the program is modified to read :

     /* floaterr.c--demonstrates round-off error */
     # include <stdio.h>
     main()
       {
         float a,b;
         b = 2.0e20 + 1.0;
         a = 2.0e20;
         printf("%f \n",b - a);
       }

  The program returns 0.000000 . Why ?