>  I just got the MSVC++ program and was
> trying out your sample programs on your web page. However, when I tried the
> prime number program it gave me this error:
> 
> C:\My Documents\My Programs\p1.cpp(15) : error C2374: 'i' : redefinition;
> multiple initialization
>         C:\My Documents\My Programs\p1.cpp(12) : see declaration of 'i'
> 
> How would this error be fixed so that the program works under MSVC++?
> 


Thanks for pointing this out.  The "error" occurs because the 
installation of MSVC++ that you were using (which may be the same as
in the Lab) has not yet been updated to conform to the new C++ standard.

Here is the code you've referred to:

>   for (int i = 2; i <= s/2; ++i)  // Sieve of Eratosthenes  (up to s)
>     if ( primes[i] )
>        for (int j = 2*i; j <= s; j+=i)
> 	   primes[j] = 0;
> 
>   for (int i = 2; i <= s && i < N; ++i)       //  Check primality of N.
>     if ( primes[i] )
>        if ( !(N%i) )
>        {
>          factor = i;
>          break;
>        }

Note that I have defined i twice in this fragment; once for each for-loop.
In the original definition of C++, the scope of a variable declared
inside the header of a "for" loop (like i) extended to the end of the 
block *in which the "for" loop occurred.*   Your installation is using 
this original, outdated rule.  Under that rule, the above fragment
makes the error of defining i twice in the same scope.

In the most recent definition of C++, the scope of a variable declared
inside the header of a "for" loop extends only to the end of the 
"for" loop body.   This is the definition assumed by my example, and
it's the definition used by the compiler I tested my code on.

The code can easily be changed so that it works with both standards:

>   int i;
>   for (i = 2; i <= s/2; ++i)  // Sieve of Eratosthenes  (up to s)
>     if ( primes[i] )
>        for (int j = 2*i; j <= s; j+=i)
> 	   primes[j] = 0;
> 
>   for (i = 2; i <= s && i < N; ++i)       //  Check primality of N.
>     if ( primes[i] )
>        if ( !(N%i) )
>        {
>          factor = i;
>          break;
>        }

File p2.cpp, posted 10/21/99, incorporates this modification and
compiles and runs under the default installation of MSVC++.
I will try to find out how we can configure the compilers in the lab
to better support the new C++ standard.  In the meantime, it may
be best to declare (index) variables outside of loop headers.