AllFun.h

#include <stdio.h>
#include <stdlib.h>     // malloc()
#include <stddef.h>   // NULL
#define MaxSize 10

typedef int ElemType;
typedef struct node {
	ElemType  data;
	struct node* lchild, * rchild;
} *BiTNode;

typedef struct stack {
	BiTNode PArray[MaxSize];
	int top;
} Stack;

typedef struct queue {
	BiTNode PArray[MaxSize];
	int front, rear;
} Queue;

BiTNode create();
void InvertLevel(BiTNode T);

MainFunc.c

#include "AllFun.h"
int main(int argc, char* argv[])
{
	BiTNode T;
	T = create();
	InvertLevel(T);
	return 0;
}

OtheFunc.c

#include "AllFun.h"

BiTNode newNode(ElemType x)
{
	BiTNode T = (BiTNode)malloc(sizeof(struct node));
	if (T) {
		T->data = x;
		T->lchild = T->rchild = NULL;
	}
	return T;
}

void insert(BiTNode* T, ElemType x)
{
	if (*T == NULL) {
		*T = newNode(x);
		return;
	}
	if (x < (*T)->data) {
		insert(&(*T)->lchild, x);
	}
	else {
		insert(&(*T)->rchild, x);
	}
}

BiTNode create()
{
	ElemType num[MaxSize];
	BiTNode T = NULL;
	for (int i = 0; i < MaxSize; ++i) {
		num[i] = ' ';
	}
	printf("Enter some value to create a binary search tree: ");
	for (int i = 0; i < MaxSize; ++i) {
		scanf_s("%d", &num[i]);
		insert(&T, num[i]);
	}
	return T;
}

InitStack(Stack* s)
{
	s->top = -1;
}

InitQueue(Queue* Q)
{
	Q->front = Q->rear = 0;
}

void EnQueue(Queue* Q, BiTNode bt)
{
	if ((Q->rear + 1) % MaxSize == Q->front) {
		return;
	}
	Q->PArray[Q->rear] = bt;
	Q->rear = (Q->rear + 1) % MaxSize;
	return;
}

int IsQEmpty(Queue* Q)
{
	int ret = 0;
	if (Q->rear == Q->front) {
		ret = 1;
	}
	return ret;
}

void DeQueue(Queue* Q, BiTNode* p)
{
	if (Q->rear == Q->front) {
		return;
	}
	*p = Q->PArray[Q->front];
	Q->front = (Q->front + 1) % MaxSize;
	return;
}

void Push(Stack* s, BiTNode p)
{
	if (s->top == MaxSize - 1) {
		printf("stack is full, push fail\n");
	}
	else {
		s->PArray[++s->top] = p;
	}
	return;
}

int IsSEmpty(Stack* s)
{
	int ret = 0;
	if (s->top == -1) {
		ret = 1;
	}
	return ret;
}

void Pop(Stack* s, BiTNode* p)
{
	if (s->top == -1) {
		printf("stack is empty, pop fail\n");
		return;
	}
	*p = s->PArray[s->top--];
	return;
}

void visit(BiTNode p)
{
	printf("%d ", p->data);
}

void InvertLevel(BiTNode bt)
{
	Stack s;
	Queue Q;
	BiTNode p = NULL;
	if (bt != NULL) {
		InitStack(&s);
		InitQueue(&Q);
		EnQueue(&Q, bt);
		while (!IsQEmpty(&Q)) {
			DeQueue(&Q, &p);
			Push(&s, p);
			if (p->lchild) {
				EnQueue(&Q, p->lchild);
			}
			if (p->rchild) {
				EnQueue(&Q, p->rchild);
			}
		}   // while
		while (!IsSEmpty(&s)) {
			Pop(&s, &p);
			visit(p);
		}
	}   // if
}