c - Cannot print out data in a binary tree -

actually, here asking debug. so, if don't have interest in helping me debugging, can stop here go back. however, believe code contain small bug because have tested part of it.

i have little test myself. code work when commented out function pinrtonenode(), mean input data binary tree. bug in printonrnode() function.

and also, compile time error is

c:\users\...\local\temp\ccwcuby.oprompt c:\users\...\.../bst.c:45printonenode  collect2.exe:error:ld returned 1 exit status 

by way, bst.c source code in

so here code:

#include<stdio.h> #include<string.h> #include<stdlib.h>  typedef struct bstnode{     struct bstnode* leftchild;     struct bstnode* rightchild;     char data[20]; }bstnode;  void prompt();        //this function prompt user selection everytime                      //after input data( inputdata() ) or print data( printonenode() )  void inputdata(); void printonenode();  bstnode firstnode; bstnode* mynode=&firstnode;   //i don't know if it's initialize way  int main() {    //mynode=malloc(sizeof(bstnode));    mynode->leftchild=null;    mynode->rightchild=null;    strcpy(mynode->data,"");    while(1)       prompt();        // use while loop prompt user selection continuously    return 0; }  /* function used prompt user selection input*/ void prompt(){    int i=0;         printf("please select:\n");    printf("1.input data\n2.print 1 data\n3.exit\n");     scanf("%d",&i);    switch(i){      case 1:          inputdata();          break;      case 2:          printonenode();          break;      case 3:          exit(0);      default:          printf("please input valid number!(1-3)");    }  }  /* used input data binary tree*/ void inputdata(){    char data[20]={0};    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; }  /* used print data, 1 @ time*/ void printonenode(){     bstnode** ptr=&mynode;     printf("the first node is%s\n",(*ptr)->data);     while(1){         printf("select side of node want print now(l/r)?(q quit) "); //i ask user whether wanna print out data in node in right side // of current node or left side          char a;         scanf("%c",&a);         switch(a){             case 'l':                 if((*ptr)->leftchild!=null){                     ptr=&((*ptr)->leftchild);                     printf("\t%s\n",(*ptr)->data);                     }                 else                     printf("there no more leftchild");                 break;             case 'r':                  if((*ptr)->rightchild!=null){                     ptr=&((*ptr)->rightchild);                     printf("\t%s\n",(*ptr)->data);                 }                 else                     printf("there no more rightchild!");                 break;             case 'q':               return;            default:               return;       }    } } 

please help. , improvement snippet of code beside bug appreciated vert much. thanks.