逆波兰式（后缀表达式）的计算

输入 ：后缀表达式（可带浮点数）

输出：double型的计算结果

代码：

#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#define ElemType double
#define Stack_Init_Size 100
#define Increase_Size 10
#define MaxBuffer 10
typedef struct sqStack
{
    ElemType *top;
    ElemType *base;
    int initSize;
}sqStack;
typedef struct sqStack *LinkStack;

//初始化
void InitStack( sqStack *s )
{
    s->base = (LinkStack)malloc(Stack_Init_Size * sizeof(ElemType));
    if(!s->base)
    {
        printf("存储空间分配失败······
");
        return;
    }
    s->top = s->base;
    s->initSize = Stack_Init_Size;
}
//进栈
void Push(sqStack *s,ElemType e)
{
    if(s->top - s->base >= s->initSize - 1)
    {
        s->base = (LinkStack)realloc(s->base,(s->initSize + Increase_Size) * sizeof(ElemType));
        //第一个s->base是增加后的存储空间块的地址，第二个是增加空间之前的存储空间块地址，后面是增加过的存储空间块的大小
        if(!s->base)
        {
            printf("增加存储空间失败······
");
            return;
        }
        s->initSize = Increase_Size + Stack_Init_Size;
    }
    *(s->top) = e;
    (s->top)++;
}
//出栈
void Pop(sqStack *s,ElemType *e)
{
    if(s->top == s->base)
    {
        printf("栈已空，无法进行出栈操作······
");
        return;
    }
    s->top--;
    *e = *s->top;
}
//求栈的长度
int StackLen(sqStack s)
{
    return (s.top - s.base);
}

//逆波兰计算器：输入逆波兰式（后缀表达式）输出结果
int main()
{
    int i = 0,j,len;
    double m,n,t;
    char c;
    struct sqStack s;
    char str[MaxBuffer];
    InitStack(&s);
    printf("请输入您要计算的后缀表达式，按Enter键结束（两个不同的字符之间用空格隔开）：
");
    scanf("%c",&c);
    while(c != '
')
    {
        while( (c >= '0'&&c <= '9') || c == '.')
        {
            str[i] = c;
            i++;
 //           str[i] = '';
            if(i >= 10)
            {
                printf("
输入的数字过大导致出错！！！
");
                return -1;
            }
            scanf("%c",&c);
           if( c == ' ')
           {
               t = atof(str);
 //              printf("
t is %f
",t);
               Push(&s,t);
               i = 0;
               for(j = 0;j < MaxBuffer;j++)
               {
                   str[j] = '';
               }
               break;
           }

        }
        switch( c )
        {
            case '+':
                Pop(&s,&m);
                Pop(&s,&n);
                Push(&s,n+m);
                break;
            case '-':
                Pop(&s,&m);
                Pop(&s,&n);
                Push(&s,n-m);
                break;
            case '*':
                Pop(&s,&m);
                Pop(&s,&n);
                Push(&s,n*m);
                break;
            case '/':
                Pop(&s,&m);
                Pop(&s,&n);
                if( m == 0)
                {
                    printf("
除数为0，出错！！！
");
                    return -1;
                }
                else
                {
                    Push(&s,n/m);
                    break;
                }
        }

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

    Pop(&s,&t);
    printf("
最终的计算结果为：%f 
",t);
    return 0;
}