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From: DFS <nospam@dfs.com>
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Subject: Re: Suggested method for returning a string from a C program?
Date: Sun, 23 Mar 2025 12:29:49 -0400
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On 3/22/2025 2:32 PM, Lynn McGuire wrote:
> On 3/18/2025 8:38 PM, DFS wrote:
>>
>> 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;
>> }
>> ------------------------------------------------------------
>>
>> Any ideas?
>> Thanks
> 
> strdup.
>     https://www.geeksforgeeks.org/strdup-strdndup-functions-c/
> 
> Lynn



The main issue, quickly spotted by Keith Thompson, was the program was 
supposed to read input from stdin.  I had it reading from the command 
line (so no output), and using an int where long was needed (returned 
some wrong answers).


Thanks.