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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Suggested method for returning a string from a C program?
Date: Wed, 19 Mar 2025 12:52:16 -0700
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DFS <nospam@dfs.com> writes:

> On 3/19/2025 1:27 AM, Tim Rentsch wrote:
>
>> DFS <nospam@dfs.com> writes:
>>
>>> On 3/18/2025 11:07 PM, Tim Rentsch wrote:
>>>
>>>
>>>> Have you thought about how large the value of 'n' can
>>>> become inside the while() loop?
>>>
>>> I was too smug in my first reply.  [...]
>>
>> Yes, I knew that already.  Did you think I asked the question
>> without having first investigated the problem?
>
> I wouldn't presume.
>
> Did you investigate first?

Of course.

> I just now did:
>
> gcc on Kali Linux (in Windows WSL)
>
> run it:  $ ./weird start stop
>
> $time ./weird 1 1000000
> <1000000 lines will be output>
> max n = 56991483520 reached at input = 704511
>
> real    0m5.792s
>
>
>
> code
> -----------------------------------------------------------------
> // If n is even, divide it by two.
> // If n is odd, multiply it by three and add one.
> // Repeat until n is one.
> // example:  the sequence for n=3 is  3 10 5 16 8 4 2 1
>
> #include <stdio.h>
> #include <stdlib.h>
>
> int main(int argc, char *argv[])
> {
> int steps, input;
> int startN = atoi(argv[1]);
> int stopN  = atoi(argv[2]);
> int64_t n = 0, max = 0, thismax = 0;
>
> for (int i = startN; i <= stopN; i++) {
>
>         n = i;
>         steps = 1;
>         thismax = n;
>         while(1) {
>
>             if((n % 2) == 0)
>                 {n /= 2;}
>             else
>                 {n = (n * 3) + 1;}
>
>             if (n > max)     {max = n; input = i;}
>             if (n > thismax) {thismax = n;}
>             steps++;
>
>             if (i == 1) {
>                 printf("input 1, max n =      1, steps =    1\n");
>                 break;
>             }
>
>             if(n == 1) {
>                 printf("input %d, max n = %6lld, steps = %4d\n",
>                     i, thismax, steps);
>                 break;
>             }
>         }
>
>
> }
> printf("\nmax n = %lld reached at input = %d\n", max, input);
> return 0;
> }
>
> -----------------------------------------------------------------
>
> You'll get compilation warnings about the printf specifier used with
> int64_t.

I recommend using unsigned long long rather than int64_t.  After
all, all values reached are guaranteed to be non-negative.  And
there is no confusion or uncertainty about what conversion sequence
to use in the call to printf().