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From: DFS <nospam@dfs.com>
Newsgroups: comp.lang.c
Subject: Re: Suggested method for returning a string from a C program?
Date: Tue, 18 Mar 2025 22:43:47 -0400
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On 3/18/2025 10:05 PM, Keith Thompson wrote:
> DFS <nospam@dfs.com> writes:
>> I'm doing these algorithm problems at
>> https://cses.fi/problemset/list/
>>
>> For instance: Weird Algorithm
>> https://cses.fi/problemset/task/1068
>>
>> My code works fine locally (prints the correct solution to the
>> console), but when I submit the .c file the auto-tester flags it with
>> 'runtime error' and says the output is empty.
>>
>> ------------------------------------------------------------
>> // If n is even, divide it by two.
>> // If n is odd, multiply it by three and add one.
>> // Repeat until n is one.
>> // n = 3: output is 3 10 5 16 8 4 2 1
>>
>>
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <string.h>
>>
>> int main(int argc, char *argv[])
>> {
>>      int n = atoi(argv[1]);
>>      int len = 0;
>>      char result[10000] = "";
>>      sprintf(result, "%d ", n);
>>
>>      while(1) {
>>          if((n % 2) == 0)
>>              {n /= 2;}
>>          else
>>              {n = (n * 3) + 1;}
>>
>>          if(n != 1)
>>              {
>>                  len = strlen(result);
>>                  sprintf(result + len, "%d ", n);
>>              }
>>          else
>>              break;
>>      }
>>
>>      len = strlen(result);
>>      sprintf(result + len, "1 ");
>>      printf("%s\n",result);
>>
>>      return 0;
>> }
>> ------------------------------------------------------------
> 
> I don't see any problem with the code, and neither does gcc on
> my system.  

It also compiles cleanly on theirs.


> But the code you posted contains a number of NO-BREAK
> SPACE characters (0xa0).  "clang -Wno-unicode-whitespace" accepts
> those characters without complaint, and gives non-fatal warnings
> without that option.  gcc treats them as a fatal error.

Those were probably added by one of our newsreaders.

Here's what it looks like on Notepad++ (showing end of line symbols)

https://imgur.com/DTX9fZG


> A minor point: You print a trailing space.  I don't know whether
> the auto-tester will accept that.

I removed that, and no such luck.


Thanks for looking at it.