排序二叉树的中序遍历

http://acm.sdut.edu.cn/sdutoj/problem.php?action=showproblem&problemid=2128

#include<stdio.h>   
#include<malloc.h>   
typedef struct tree   
{   
    int data; 
    struct tree *l,*r;   
}tree;   
int k;   
void creat(tree *t,int a)   
{   
    tree *p;   
    p = (tree *)malloc(sizeof(tree));   
    p->data = a;   
    if(t->data>a)   
    {   
         if(t->l == NULL)   
         {   
             t->l = p;   
             p->l = NULL;   
             p->r = NULL;   
         }   
         else  
             creat(t->l,p->data);   
    }   
    else  
    {   
        if(t->r == NULL)   
         {   
             t->r = p;   
             p->l = NULL;   
             p->r = NULL;   
         }   
         else  
             creat(t->r,p->data);   
    }   
}   
void midsearch(tree *t)   
{   
    if(t!=NULL)   
    {          
        midsearch(t->l);   
        if(k!=0)   
            printf(" ");   
        printf("%d",t->data);   
        k++;   
        midsearch(t->r);   
    }   
}   
int main()   
{   
    int n,i,a;   
    tree *t;   
    t = (tree *)malloc(sizeof(tree));   
    while(scanf("%d",&n)!=EOF)   
    {   
        k = 0;   
        for(i = 1 ;i <= n ; i++)   
        {   
            scanf("%d",&a);   
            if(i == 1)   
            {   
                t->data = a;   
                t->l = NULL;   
                t->r = NULL;   
            }   
            else  
                creat(t,a);   
        }   
        midsearch(t);   
        printf("\n");   
    }   
    return 0;   
}