利用后缀表达式的思想，输入一个字符串，计算其值。

• 计算方案

#include "LinkStack.h"

int priority(char ch)
{
	switch(ch)
	{
		case '(':
			return 3;
		case '*':
		case '/':
			return 2;
		case '+':
		case '-':
			return 1;
		default :
			return 0;
	}
}

int main()
{
	char opt[1024] = {0};
	int num1 = 0, num2 = 0, i = 0, tmp = 0;
	Stack *s_num = NULL, *s_opt = NULL;
	
	if(StackInit(&s_num) !=SUCCESS || StackInit(&s_opt)	!= SUCCESS)
	{
		printf("Stack Init Error\n");
		return 0;
	}
	
	printf("Please input:\n");
	scanf("%s", opt);
	
	while(opt[i] != '\0' || StackEmpty(s_opt) != TRUE)
	{
		if(opt[i] >= '0' && opt[i] <= '9')
		{
			tmp = tmp*10 + opt[i]-'0';
			i++;
			if(opt[i] < '0' || opt[i] > '9')
			{
				Push(&s_num, tmp);
				tmp = 0;
			}
		}
		else
		{
			if(opt[i] == ')' && GetTop(s_opt) == '(')
			{
				Pop(&s_opt);
				i++;
				continue;
			}
			
			if(StackEmpty(s_opt) == TRUE ||
			   (GetTop(s_opt) == '(' && opt[i] != ')') ||
			   (priority(opt[i]) > priority(GetTop(s_opt))) )
			{
				Push(&s_opt, opt[i]);
				i++;
				continue;
			}
			
			if((opt[i] == '\0' && StackEmpty(s_opt) != TRUE)||
			   (opt[i] == ')' && GetTop(s_opt) != '(') ||
			   ( priority(opt[i]) <= priority( GetTop(s_opt) ) ) )
			{
				switch(Pop(&s_opt))
				{
					case '+':
						num1 = Pop(&s_num);
						num2 = Pop(&s_num);
						Push(&s_num, num1+num2);
						break;
					case '-':
						num1 = Pop(&s_num);
						num2 = Pop(&s_num);
						Push(&s_num, num2-num1);
						break;
					case '*':
						num1 = Pop(&s_num);
						num2 = Pop(&s_num);
						Push(&s_num, num1*num2);
						break;
					case '/':
						num1 = Pop(&s_num);
						num2 = Pop(&s_num);
						Push(&s_num, num2/num1);
						break;
				}
			}
		}
	}
	
	printf("%d\n", GetTop(s_num));
	return 0;
}

• 头文件：

#ifndef _LINKSTACK_H
#define _LINKSTACK_H

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

#define SUCCESS 10000
#define FAILURE 10001
#define TRUE    10002
#define FALSE   10003

typedef int Elemtype;

typedef struct node
{
	Elemtype data;
	struct node *next;
}Node;

typedef struct stack
{
	struct node *top;
	int count;
}Stack;

int StackInit(Stack **stack);
int StackEmpty(Stack *stack);
int Push(Stack **stack, Elemtype e);
int GetTop(Stack *stack);
int Pop(Stack **stack);
int StackClear(Stack **stack);
int StackDestory(Stack **stack);

#endif

• 功能函数：

#include "LinkStack.h"

int StackInit(Stack **stack)
{
	if(NULL == stack)
	{
		return FAILURE;
	}
	
	*stack = (Stack *)malloc(sizeof(Stack)*1);
	if(NULL == *stack)
	{
		return FAILURE;
	}
	
	(*stack)->top = NULL;
	(*stack)->count = 0;
	
	return SUCCESS;
}

int StackEmpty(Stack *stack)
{
	if(NULL == stack)
	{
		return FAILURE;
	}
	
	return (stack->top == NULL) ? TRUE : FALSE;
}

int Push(Stack **stack, Elemtype e)
{
	if(NULL == stack || NULL == *stack)
	{
		return FAILURE;
	}
	
	Node *p;
	p = (Node *)malloc(sizeof(Node));
	if(NULL == p)
	{
		return FAILURE;
	}
	
	p->data = e;
	p->next = (*stack)->top;
	(*stack)->top = p;
	(*stack)->count++;

	return SUCCESS;	
}

int GetTop(Stack *stack)
{
	if(NULL == stack)
	{
		return FAILURE;
	}
	
	return stack->top->data;
}

int Pop(Stack **stack)
{
	if(NULL == stack || NULL == *stack)
	{
		return FAILURE;
	}
	
	Node *p = (*stack)->top;
	Elemtype e = (*stack)->top->data;
	
	(*stack)->top = (*stack)->top->next;
	(*stack)->count--;
	free(p);
	p = NULL;
	
	return e;
}

int StackClear(Stack **stack)
{
	if(NULL == stack || NULL == *stack)
	{
		return FAILURE;
	}
	
	Node *p;
	
	while((*stack)->top != NULL)
	{
		p = (*stack)->top;
		(*stack)->top = (*stack)->top->next;
		(*stack)->count--;
		free(p);
	}
	return SUCCESS;
}

int StackDestory(Stack **stack)
{
	if(NULL == stack || NULL == *stack)
	{
		return FAILURE;
	}
	
	Node *p;
	
	while((*stack)->top != NULL)
	{
		p = (*stack)->top;
		(*stack)->top = (*stack)->top->next;
		(*stack)->count--;
		free(p);
	}
	
	free(*stack);
	*stack = NULL;
	
	return SUCCESS;
}