c - How does toggling a call to printf within a function determine whether my code doesn't crash? -

i writing simple function creates new node @ beginning of linked list. when try execute file windows command error window comes saying "a.exe has stopped working."

what mystery me when add printf call within body of insertnewnodeatfront, code executes without above error box. ideas?

here source file:

#include <stdio.h>   typedef struct nodetag{     const char* airport;     struct nodetag * link;                     } nodetype;   void insertnewnodeatfront(nodetype *, const char*);   void insertnewnodeatfront(nodetype * l,  const char* str){      nodetype * n;     n = l;         nodetype * newfirst;     newfirst->airport = str;     newfirst->link = n;     l = newfirst;    //printf("l->airport: %s\n",l->airport); <---this line magically makes work. }  int main(){     nodetype * myitinerary;     insertnewnodeatfront(myitinerary,"ont");     return 0; } 

as hmjd has said, crash caused using uninitialised memory. reason doesn't crash @ point when add more code causes compiler move things around in memory, uninitialised variable points somewhere different.

it still bad, however: code has still blatted random location in memory cause crash time.