二叉树的广度优先遍历（又称层序遍历）需要使用队列（通常用链表实现）来完成。以下是实现的代码，分为三个文件：function.h、queue.cpp 和 main.cpp。
1.function.h
#include<stdio.h>
#include<stdlib.h>
//二叉树的函数声明
typedef char elemtype;
typedef struct bitree {elemtype tdata;struct bitree* lchild, * rchild;
}bitree, * pbitree;
typedef struct tag {pbitree p;//指向某一个二叉树指针struct tag* next;
}tag, * ptag;//辅助队列函数声明
typedef struct node{pbitree data;struct node *next;
}node;
typedef struct sq_queue {node* front, * rear;
}sq_queue;
void init_queue(sq_queue& Q);
bool is_empty(sq_queue Q);
void en_queue(sq_queue &Q,pbitree x);
void de_queue(sq_queue &Q, pbitree &keep);
2.queue.cpp（辅助队列的实现）
#include"function.h"
void init_queue(sq_queue& Q)
{Q.front = Q.rear = (node*)calloc(1, sizeof(node));Q.front->next = NULL;
}
bool is_empty(sq_queue Q)
{if (Q.rear == Q.front){return true;}return false;
}
void en_queue(sq_queue &Q,pbitree x)
{node* s = (node*)calloc(1, sizeof(node));s->data = x;s->next = NULL;Q.rear->next = s;Q.rear = s;
}
void de_queue(sq_queue& Q, pbitree& keep)
{node* p = Q.front->next;keep = p->data;Q.front->next = p->next;if (Q.rear == p){Q.rear = Q.front;}free(p);
}
3.main.cpp（层序遍历的实现）
#include"function.h"
void level_order(pbitree tree)
{sq_queue Q;init_queue(Q);pbitree keep;en_queue(Q, tree);//将根节点入队while (!is_empty(Q)){de_queue(Q,keep);putchar(keep->tdata);if (keep->lchild != NULL){en_queue(Q, keep->lchild);//将左孩子入队}if (keep->rchild != NULL){en_queue(Q, keep->rchild);//将右孩子入队}}
}
int main()
{//二叉树建树pbitree pnew;pbitree tree = NULL;elemtype c;ptag head = NULL, tail = NULL, pcur = NULL, link_new = NULL;while (scanf("%c", &c)){if (c == '\n'){break;}pnew = (pbitree)calloc(1, sizeof(bitree));pnew->tdata = c;link_new = (ptag)calloc(1, sizeof(tag));link_new->p = pnew;if (tree == NULL){tree = pnew;head = link_new; tail = link_new;pcur = link_new; link_new = link_new;continue;}else{tail->next = link_new;tail = tail->next;}if (pcur->p->lchild == NULL){pcur->p->lchild = pnew;}else if(pcur->p->rchild == NULL){pcur->p->rchild = pnew;pcur = pcur->next;}}level_order(tree);//层序遍历（广度优先遍历）}
