Cannot print out data in a binary tree - c

Question

Actually, I am here asking you to help debug. So, if you don't have any interest in helping me debugging, you can stop here any go back. However, I believe that my code only contain a small bug because I have tested most part of it.
I have do a little test myself. The code work successfully when I commented out the function pinrtOneNode(), which mean that I only input data into that binary tree. So probably the only bug is in the printOnrNode() function.
And also, the compile time error is
c:\users\...\Local\temp\ccwCUbY.oprompt
c:\users\...\.../bst.c:45printOneNode
collect2.exe:error:ld returned 1 exit status
By the way, the bst.c is where my source code in
So here is the 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 always prompt the user for selection everytime
//after he input data( inputData() ) or print data( printOneNode() )
void inputData();
void printOneNode();
BSTnode firstNode;
BSTnode* MyNode=&firstNode; //I don't know if it's good to initialize it this way
int main()
{
//MyNode=malloc(sizeof(BSTnode));
MyNode->leftchild=NULL;
MyNode->rightchild=NULL;
strcpy(MyNode->data,"");
while(1)
prompt(); // I use a while loop to prompt user for selection continuously
return 0;
}
/* this function is used to prompt user for selection input*/
void prompt(){
int i=0;
printf("Please select:\n");
printf("1.input a data\n2.print only one 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 a valid number!(1-3)");
}
}
/* this is used to input data into the binary tree*/
void inputData(){
char data[20]={0};
printf("Input your data here(character only / less than 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(" Your data have been input successfully!\n");
return;
}
/* this is used to print data, only one at a time*/
void PrintOneNode(){
BSTnode** ptr=&MyNode;
printf("The first node is%s\n",(*ptr)->data);
while(1){
printf("Select which side of node do you want to print now(l/r)?(q for quit) ");
//I ask user whether he wanna print out the data in node in the right side
// of the 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 is no more leftchild");
break;
case 'r':
if((*ptr)->rightchild!=NULL){
ptr=&((*ptr)->rightchild);
printf("\t%s\n",(*ptr)->data);
}
else
printf("There is no more rightchild!");
break;
case 'q':
return;
default:
return;
}
}
}
Please help. And any improvement to this snippet of code beside the bug will be also appreciated vert much. Thanks.