数据结构--栈的应用

 要求：首先将操作数栈opnd设为空栈，而将'#'作为运算符栈opter的栈底元素，这样的目的是判断表达式是否求值完毕；（2）依次读入表达式的每个字符，表达式须以'#'结尾，若是操作数则入栈opnd，若是运算符,则将此运算符c与opter的栈顶元素top比较优先级后执行相应的操作，具体操作如下：(i)若top的优先级小于c，即top<c，则将c直接入栈opter，并读入下一字符赋值给c；(ii)若top的优先级等于c，即top=c，则弹出opter的才顶元素，并读入下一字符赋值给c，这一步目的是进行括号操作。

#include <stdio.h>
#include <stdlib.h>
#define STACK_INIT_SIZE 100
#define STACKINCREMENT 10
typedef struct{
	char *base;
	char *top;
	int stacksize;
}SqStack;

typedef struct{
	int *base;
	int *top;
	int stacksize;
}SqStacknum;
int InitStack(SqStack *S)
{
	S->base = (char *)malloc(STACK_INIT_SIZE * sizeof(char));
	if (!S->base) exit(0);
	S->top = S->base;
	S->stacksize = STACK_INIT_SIZE;
	return 1;
}
int InitStacknum(SqStacknum *S)
{
	S->base = (int *)malloc(STACK_INIT_SIZE * sizeof(int));
	if (!S->base) exit(0);
	S->top = S->base;
	S->stacksize = STACK_INIT_SIZE;
	return 1;
}
char GetTop(SqStack S)
{
	char e;
	if (S.top == S.base) return 0;
	e = *(S.top - 1);
	return e;
}
int GetTopnum(SqStacknum S)
{
	int e;
	if (S.top == S.base) return 0;
	e = *(S.top - 1);
	return e;
}
int Push(SqStack *S, char e)
{
	if (S->top - S->base >= S->stacksize)
	{
		S->base = (char *)realloc(S->base,
			(S->stacksize + STACKINCREMENT) * sizeof(char));
		if (!S->base) exit(0);
		S->top = S->base + S->stacksize;
		S->stacksize += STACKINCREMENT;
	}
	*S->top++ = e;
	return 1;
}
int Pushnum(SqStacknum *S, int e)
{
	if (S->top - S->base >= S->stacksize)
	{
		S->base = (int *)realloc(S->base,
			(S->stacksize + STACKINCREMENT) * sizeof(int));
		if (!S->base) exit(0);
		S->top = S->base + S->stacksize;
		S->stacksize += STACKINCREMENT;
	}
	*S->top++ = e;
	return 1;
}
int Pop(SqStack *S, char *e)
{
	if (S->top == S->base) return 0;
	*e = *--S->top;
	return 1;
}
int Popnum(SqStacknum *S, int *e)
{
	if (S->top == S->base) return 0;
	*e = *--S->top;
	return 1;
}
int Operate(int a, char theta, int b)
{
	switch (theta)
	{
	case '+':
		return a + b;
	case '-':
		return a - b;
	case '*':
		return a * b;
	case '/':
		return a / b;
	}
	//printf("No this theta");
	//printf("%c^",theta);
}
int In(char c)
{
	switch (c)
	{
	case '+':
		return 0;
	case '-':
		return 0;
	case '*':
		return 0;
	case '/':
		return 0;
	case '(':
		return 0;
	case ')':
		return 0;
	case '#':
		return 0;
	}
	return 1;
}
int getIndex(char theta)   //获取theta所对应的索引
{
	int index = 0;
	switch (theta)
	{
	case '+':
		index = 0;
		break;
	case '-':
		index = 1;
		break;
	case '*':
		index = 2;
		break;
	case '/':
		index = 3;
		break;
	case '(':
		index = 4;
		break;
	case ')':
		index = 5;
		break;
	case '#':
		index = 6;
	default:break;
	}
	return index;
}
char getPriority(char theta1, char theta2)   //获取theta1与theta2之间的优先级
{
	const char priority[][7] =     //算符间的优先级关系
	{
		{ '>', '>', '<', '<', '<', '>', '>' },
		{ '>', '>', '<', '<', '<', '>', '>' },
		{ '>', '>', '>', '>', '<', '>', '>' },
		{ '>', '>', '>', '>', '<', '>', '>' },
		{ '<', '<', '<', '<', '<', '=', '0' },
		{ '>', '>', '>', '>', '0', '>', '>' },
		{ '<', '<', '<', '<', '<', '0', '=' },
	};
	int index1 = getIndex(theta1);
	int index2 = getIndex(theta2);
	return priority[index1][index2];
}
int main()
{
	char theta, c, x, l;
	int a, b;
	SqStack OPTR;
	SqStacknum OPND;
	printf("please input some things\n");
	InitStack(&OPTR); //运算符
	Push(&OPTR, '#'); //操作数
	InitStacknum(&OPND);
	c = getchar();
	while (c != '#' || GetTop(OPTR) != '#')
	{
		if (In(c))
		{
			Pushnum(&OPND, (int)c - 48);
			c = getchar();
		}
		else
		{
			switch (getPriority(GetTop(OPTR), c))
			{

			case '<':
				Push(&OPTR, c);
				c = getchar();
				break;
			case '=':
				Pop(&OPTR, &x);
				c = getchar();
				break;
			case '>':
				Pop(&OPTR, &theta);
				Popnum(&OPND, &b);
				Popnum(&OPND, &a);
				Pushnum(&OPND, Operate(a, theta, b));
				break;
			}
		}
	}
	printf("%d", GetTopnum(OPND));
}