【中缀表达式转后缀表达式】

#include<iostream>
#include<string>
#include<cmath>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<ctype.h>
using namespace std;
const int maxn = 1000 + 10;
typedef char TypeName;
struct node {
	TypeName num;
	struct node *next;
};
typedef struct node Link;
static Link *head;
int isEmpty()
{
	return head == NULL;
}
void StackInit()
{
	head = NULL;
}
Link * NEW(TypeName num, Link *head)
{
	Link *t = (Link *)malloc(sizeof(Link));
	t->num = num;
	t->next = head;
	return t;
}
void StackPush(TypeName num)
{
	head = NEW(num, head);
}
TypeName StackPop()
{
	TypeName num = head->num;
	Link *t = head->next;
	free(head);
	head = t;
	return num;
}
int main()
{
	string str;
	while (cin >> str)
	{
		int len = str.length();
		for (int i = 0;i < len;i++)
		{
			char ch = str[i];
			if (ch == '(') continue;
			if (isdigit(ch)) cout << ch << " ";
			else if (ch == ')') cout << StackPop();
			else
				StackPush(ch);
		}
		cout << endl;
	}
	system("pause");
	return 0;
}

【后缀表达式求值】

int main()
{
	char str[maxn];
	while (cin >> str)
	{
		int len = strlen(str);
		StackInit();
		for (int i = 0;i < len;i++)
		{
			char ch = str[i];
			if (ch == '*') StackPush(StackPop() * StackPop());
			if (ch == '+') StackPush(StackPop() + StackPop());
			if (isdigit(ch))
				StackPush(0);
			while (isdigit(str[i]))
				StackPush(StackPop() * 10 + str[i++] - '0');
		}
		cout << StackPop() << endl;
	}
	system("pause");
	return 0;
}