C: Why can't I change the top binary tree node in a non-main method? -

i think more of pointer problem binary tree problem. exercise re-creating guessing/learning game in c using binary tree. had method, traverse, go through tree , ask questions, etc. method, when found non-existent node ask user input create node, hence learning part. when corrupted data. recreation of relevant code:

node * getnew(char *msg, char isans) {     node *nnew = malloc(sizeof(node));     nnew->id=clock();     nnew->guess=msg;     nnew->isans=isans;     nnew->yes=0;     nnew->no=0;     return nnew; } void traverse(node **top) {     char ques[128] = "ok";     char ans[128] = "ok";     printf("node null\n");     printf("put in question , answer yes condition\n");     printf("enter question: ");     while(!fgets(ques,128,stdin));     printf("enter answer yes condition: ");     while(!fgets(ans,128,stdin));     printf("check ques: %s\ncheck ans: %s\n\n",ques,ans);     make_question_answer(top,ques,ans);     fprintf(stdout,"\ncheck in method: top: %s\n\n",(*top)->guess);     fprintf(stdout,"\ncheck in method: top->yes: %s\n\n",(*top)->yes->guess); } void make_question_answer(node **change, char *ques,char *ans) {     node *top = getnew(ques,'n');     node *a = getnew(ans,'y');     top->yes=a;     top->no=(*change);     *change=top; } int main() {     node *top=0;     traverse(&top);     fprintf(stdout,"\ncheck: %s\n\n",top->yes->guess); } 

using make_question_answer() in main change top, , works in traverse won't last in jump main. points corrupted data seen fprintf. have no idea why happening.

in getnew() you're assigning nnew->guess stack variable. consider allocating memory string , using strncpy() or other mechanism fill in newly allocated memory.