#include "whead.h"
#include <stdio.h>
#include <malloc.h>
#include <iostream>


#define MAX_TREE_SIZE 100


typedef char TElemType;
//typedef TElemType SqBiTree[MAX_TREE_SIZE];

typedef struct BiTreeNode {
    TElemType data;
    struct BiTreeNode *lchild;
    struct BiTreeNode *rchild;
}BiTreeNode, *BiTree;


BiTree tm;
Status visit(TElemType v) {
    printf("node==", v);
    printf("\n");
    return OK;
}

Status createBiTreePre(BiTree t) {
    char ch;
    printf("Input char :");
    scanf("%c" ,&ch);
    printf("\n");
    if(ch == ' ')
        t = NULL;
    else {
        if(!(t = (BiTreeNode*)malloc(sizeof(TElemType))))
            exit(OVERFLOW);
        t->data = ch;
        createBiTreePre(t->lchild);
        createBiTreePre(t->rchild);
    }
    return OK;
}

Status traversePre(BiTree t, Status (*visit)(TElemType e)) {
    if(t){
        if(t->data)
            if(traversePre(t->lchild, visit))
                if(traversePre(t->rchild,visit))
                    return OK;
        return ERROR;
    }
    else
        return OK;
}



#include "BinaryTree.h"

void main() {   
    createBiTreePre(tm);
    traversePre(tm, visit);
}

为什么第一次createBiTreePre(t->lchild)无法输入，第二次就可以，第三次又不行。。。。。以此类推

    printf("Input char :");
    scanf("%c" ,&ch);
    getchar();
    printf("\n");

谢谢版主，正解。我还有比较详细的。如果谁有需要就看看

because system-Buffer of stdin

first Time you type such command in DOS, and you press [Enter] key at end of DOS-command

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1.exe //assume your program called "1.exe"

but problem comes, the Enter-key's value still has been left in SyS-buffer-input.

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printf("Input char :");
scanf("%c" ,&ch); // first time receive Enter-value from Buffer
printf("\n");

Scanf() will receive the Enter-value from system-Buffer,which is inputed last time. so scanf() already executed before you wanted input.
and created leftchild-Node.

and code continue execute to create the next left-child

The Second time
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printf("Input char :");
 
//because the last time the enter-value was got by last scanf.
//the system-buffer was cleared. this time scanf() is waiting for you input
 
scanf("%c" ,&ch);
printf("\n");

The solve. you could add a getch() before call scanf, it could receive Enter-key which has been left at last Inputing

or you could call fflush(stdin), it could clear system-buffer of stdin.

just like following code
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printf("Input char :") ;
getch() ;
scanf("%c",&ch) ;
printf("\n") ;

BY   tanakahitori