c - A binary search tree with segfault -

here want make text sorting bst structure, first text first. segfault again. sad it:

#include<stdio.h> #include<string.h> #include<stdlib.h>  typedef struct bstnode{     struct bstnode* leftchild;     struct bstnode* rightchild;     char data[20]; }bstnode;  void prompt(); void inputdata();  bstnode firstnode; bstnode* mynode=&firstnode;     //maybe there better way initialize first node  int main() {     //mynode=malloc(sizeof(bstnode));   /* initialize first node*/      mynode->leftchild=null;                   mynode->rightchild=null;     strcpy(mynode->data,"");         while(1)         prompt();                 //always prompt user input                                   //and use function store                                    //input in binary tree      return 0; }  void prompt(){     int i=0;          printf("please select:\n");     printf("1.input data\n2.exit\n");      scanf("%d",&i);     switch(i){         case 1:             inputdata();             break;         case 2:             exit(0);         default:             printf("please input valid number!(1 or 2)");     }  }  void inputdata(){     char* data="";     printf("input data here(character / less 19 characters!): ");     scanf("%s",data);     bstnode** ptr=&mynode;     while(1){         if(strcmp(data,(*ptr)->data)){             if((*ptr)->rightchild!=null){                 ptr=&((*ptr)->rightchild);                 continue;             }             else{                 (*ptr)->rightchild=malloc(sizeof(bstnode));                 ptr=&((*ptr)->rightchild);                 (*ptr)->rightchild=null;                 (*ptr)->leftchild=null;                 strcpy((*ptr)->data,data);                 break;             }         }          else{             if((*ptr)->leftchild!=null){                 ptr=&((*ptr)->leftchild);                 continue;             }             else{                 (*ptr)->leftchild=malloc(sizeof(bstnode));                 ptr=&((*ptr)->leftchild);                 (*ptr)->leftchild=null;                 (*ptr)->rightchild=null;                 strcpy((*ptr)->data,data);                 break;             }         }       }      printf(" data have been input successfully!\n");     return; } 

that code. , segfault once input word , press return. don't try print data out. want input data , store in binary search tree.

but, not skillful enough... haven't make successful bst structure. appreciate if can debug. of cource, other related information , code appreciated.

your data pointer in inputdata pointing constant (and maybe initialized somewhere in heap), shouldn't that.

you need initialize memory malloc or, use fixed-size array, f. ex.

void inputdata(){     char data[100];     memset(data,0,sizeof(data));     printf("input data here(character / less 19 characters!): ");     scanf("%s",data);     bstnode** ptr=&mynode;