[c] Segmentation Fault - C

Catastrophically bad:

int main(void){
      char *s;
      int ln;
      puts("Enter String");
      // scanf("%s", s);
      gets(s);
      ln = strlen(s); // remove this line to end seg fault
      char *dyn_s = (char*) malloc (strlen(s)+1); //strlen(s) is used here as well but doesn't change outcome
      dyn_s = s;
      dyn_s[strlen(s)] = '\0';
      puts(dyn_s);
      return 0;
    }

Better:

#include <stdio.h>
#define BUF_SIZE 80

int 
main(int argc, char *argv[])
{
      char s[BUF_SIZE];
      int ln;
      puts("Enter String");
      // scanf("%s", s);
      gets(s);
      ln = strlen(s); // remove this line to end seg fault
      char *dyn_s = (char*) malloc (strlen(s)+1); //strlen(s) is used here as well but doesn't change outcome
      dyn_s = s;
      dyn_s[strlen(s)] = '\0';
      puts(dyn_s);
      return 0;
    }

Best:

#include <stdio.h>
#define BUF_SIZE 80

int 
main(int argc, char *argv[])
{
      char s[BUF_SIZE];
      int ln;
      puts("Enter String");
      fgets(s, BUF_SIZE, stdin); // Use fgets (our "cin"): NEVER "gets()"

      int ln = strlen(s); 
      char *dyn_s = (char*) malloc (ln+1);
      strcpy (dyn_s, s);
      puts(dyn_s);
      return 0;
    }