用顺序栈解决逆波兰表达式（c语言）

定义

逆波兰表达式又叫做后缀表达式。逆波兰表示法是波兰逻辑学家J・卢卡西维兹(J・ Lukasiewicz)于1929年首先提出的一种表达式的表示方法 [1]。后来,人们就把用这种表示法写出的表达式称作“逆波兰表达式”。逆波兰表达式把运算量写在前面,把算符写在后面。

代码实现

#define _CRT_SECURE_NO_WARNINGS

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

#define beginlong 20
#define addlong 10
#define maxlong   10

typedef double elemtype;

typedef struct
{
	elemtype* base;
	elemtype* top;
	int sqlong;
}sqstack;

void initsq(sqstack* s)
{
	s->base = (elemtype*)malloc(beginlong * sizeof(elemtype));
	if (s->base == NULL)
	{
		return;
	}

	s->top = s->base;
	s->sqlong = beginlong;
}

void push(sqstack* s, elemtype e)
{
	if (s->top - s->base == s->sqlong)
	{
		s->base = (elemtype*)realloc(s->base, (addlong + s->sqlong) * sizeof(elemtype));
		if (s->base == NULL)
		{
			return;
		}
	}

	*(s->top) = e;
	s->top++;
}

void pop(sqstack* s, elemtype* e)
{
	if (s->base == s->top)
	{
		return;
	}

	*e = *--(s->top);
}

int getlong(sqstack s)
{
	return (s.top - s.base);
}

int main()
{
	sqstack s;
	char n;
	double a, b;
	int len;
	char arr[maxlong] = { 0 };
	int i = 0;

	initsq(&s);

	printf("请以逆波兰式的形式输入想求解的式子，数数之间和数符号之间加入空格,以#为结尾\n");
	scanf("%c", &n);

	while (n != '#')
	{
		while (isdigit(n) || n == '.')
		{
			arr[i] = n;
			i++;
			if (i > 9)
			{
				printf("您输入的值太大\n");
				return -1;
			}
			scanf("%c", &n);
			if (n == ' ')
			{
				a = atof(arr);
				push(&s, a);
				i = 0;
				break;
			}
		}

		switch (n)
		{
		case '-':
			pop(&s, &a);
			pop(&s, &b);
			push(&s, b - a);
			break;
		case '+':
			pop(&s, &a);
			pop(&s, &b);
			push(&s, b + a);
			break;
		case '*':
			pop(&s, &a);
			pop(&s, &b);
			push(&s, b * a);
			break;
		case '/':
			pop(&s, &a);
			pop(&s, &b);
			if (b != 0)
			{
				push(&s, b / a);
				break;
			}
			else
			{
				return -1;
			}
		}


		scanf("%c", &n);
	}

	pop(&s, &a);
	printf("%f", a);

	return 0;
}