Suggested method for returning a string from a C program?

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.
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// 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;
}
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Any ideas?
Thanks