输入字符 回车结束输入 以树的形式进行输出

#include <stdio.h>
#include <stdlib.h>

struct tree
{
    char info;
    struct tree *left;
    struct tree *right;
};

struct tree *root;        /*树的第一个结点*/
struct tree *construct(struct tree *root, struct tree *r, char info);
void print(struct tree *r, int l);

int main(void)
{
    char s[80];
    root = NULL;
    do
    {
        printf("请输入一个字符:");
        gets(s);
        root = construct(root, root, *s);
    } while (*s);
    print(root, 0);
    getchar();
    return 0;
}

struct tree *construct(
struct tree *root,
struct tree *r,
    char info)
{
    if (!r)
    {
        r = (struct tree *)malloc(sizeof(struct tree));
        if (!r)
        {
            printf("内存分配失败！");
            exit(0);
        }
        r->left = NULL;
        r->right = NULL;
        r->info = info;
        if (!root)
            return r;
        if (info < root->info)
            root->left = r;
        else
            root->right = r;
        return r;
    }
    if (info < r->info)
        construct(r, r->left, info);
    else
        construct(r, r->right, info);

    return root;
}

void print(struct tree *r, int l)
{
    int i;
    if (!r)
        return;
    print(r->left, l + 1);
    for (i = 0; i < l; ++i)
        printf(" ");
    printf("%c
", r->info);
    print(r->right, l + 1);
}