recursion - Create and traverse a binary tree recursively in C -

i want create binary tree , traverse preorder traversal, , use recursive method. these code can compiled can not run correctly, , found maybe can not finish createbitree() function, don't know problem is.

#include <stdio.h> #include <malloc.h>  typedef struct binode{     int data;     struct binode *lchild;     struct binode *rchild;    //left , right child pointer }binode;  int createbitree(binode *t); int traversebitree(binode *t);  int main() {     binode *t;     createbitree(t);     traversebitree(t);     return 0; }  int createbitree(binode *t) {          //create binary tree preorder traversal     char tmp;     scanf("%c", &tmp);     if(tmp == ' ')     t = null;     else {         t = (binode *)malloc(sizeof(binode));         t -> data = tmp;         createbitree(t -> lchild);         createbitree(t -> rchild);     }     return 1; }  int traversebitree(binode *t) {        //traverse binary tree preorder traversal     if(t != null) {         printf("%c\n", t -> data);         traversebitree(t -> lchild);         traversebitree(t -> rchild);     }     return 1; } 

for example, when input preorder sequence "abc##de#g##f###"("#"means space), , still let me input, think traversebitree() function hasn't been executed.

an assignment of pointer value pointer within function not have effect outside scope of function. doing this:

int createbitree(binode *t) {    /* ... */   t = null; 

is same doing this:

int func(int i) {    /* ... */   = 0; 

a pointer argument necessary in these cases:

int createbitree(binode **t) {    /* ... */   t[0] = null;  // or... *t = null; 

with changes initial code:

int main() {     binode *t;      createbitree(&t);     traversebitree(t);     return 0; }  int createbitree(binode **t) {          //create binary tree preorder traversal     char tmp;     scanf("%c", &tmp);     if(tmp == ' ')     t[0] = null;     else {         t[0] = (binode *)malloc(sizeof(binode));         t[0]-> data = tmp;         createbitree(&(t[0]->lchild));         createbitree(&(t[0]->rchild));     }        return 1; }