栈与队列应用：逆波兰计算器（逆波兰表达式；后缀表达式）把运算符放到运算量后边 && 中缀表达式转化为后缀表达式

//1.实现对逆波兰输入的表达式进行计算如（2-1）*（2+3）= 5  就输入2 1 - 2 3 + *   //先把2 1 压栈 遇到-弹栈 再把2 3压进去 遇到+弹栈 最后遇到*弹栈
//2.支持带小数点的数据
例： 正常操作----->逆波兰表达式
     a+b   ------>a b +
     a+(b-c)----->a b c - +
     a+(b-c)*d--->a b c - d * +
     a+d*(b-c)--->a d b c - * +

//2 5 + 4 2 - *  == （2+5）*（4-2） == 14
//1 34 + 4 2 / * ==（1+34）*（4/2）== 70 
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>  //函数isdigit  检查是否为十进制数 

#define MAXSIZE 100
#define MAXBUFFER 10 //缓冲区 

typedef double ElemType;  

typedef struct
{
    ElemType *base;
    ElemType *top;
    int sizeStack;
}sqStack;

void InitStack(sqStack *s)
{
    s->base = (ElemType *)malloc(MAXSIZE*sizeof(ElemType));
    if(!s->base)
    {
        exit(0);
    }
    s->top = s->base;
    s->sizeStack = MAXSIZE;
}

void Push(sqStack *s,ElemType e)
{
    if(s->top - s->base == s->sizeStack)
    {
        exit(0);
    }
    *(s->top) = e;
    s->top++;
}

void Pop(sqStack *s,ElemType *e)
{
    if(s->top == s->base)
    {
        return;
    }
    *e = *(--(s->top));
}
 
int main(void)
{
    sqStack s;
    char c;
    char str[MAXBUFFER];
    double d,e;
    int i = 0;
    
    InitStack(&s);
    printf("请输入后缀表达式的字符，运算符与数字用空格隔开\n");
    scanf("%c",&c);
    while(c != '#')
    {
        while(isdigit(c) || c=='.')  //判断是否遇到数字
        {
            str[i++] = c;
            str[i] = '\0';
            if(i >= 10)
            {
                printf("单个数字太大啊"); 
                return -1;
            }
            scanf("%c",&c);
            if(c == ' ')
            {
                d = atof(str);  //将字符串转换成浮点型  存在<stdlib.h>
                Push(&s,d);
                i = 0;
                break; 
            }
        }

        switch(c) //判断是否遇到运算符
        {
            case '+':
                Pop(&s,&e);
                Pop(&s,&d);
                Push(&s,d+e);
                break;
            case '-':
                Pop(&s,&e);
                Pop(&s,&d);
                Push(&s,d-e);
                break;
            case '*':
                Pop(&s,&e);
                Pop(&s,&d);
                Push(&s,d*e);
                break;
            case '/':
                Pop(&s,&e);
                Pop(&s,&d);
                if(e != 0)
                {
                    Push(&s,d/e);
                }
                else
                {
                    printf("被除数不能为0！\n");
                    return -1;
                }
                break;
        }
        scanf("%c",&c);
    }
    Pop(&s,&d);
    printf("最终结果为：%f",d);
    return 0;
}



//将中缀表达式转化为后缀表达式
#include<stdio.h>
#include<stdlib.h>

#define MAXSIZE 20
#define INCREMENTSIZE 10

typedef char ElemType; 
typedef char ElemType2;
typedef struct 
{
    ElemType *base;
    ElemType *top;
    int StackSize;
}sqStack;

void InitStack(sqStack *s)
{
    s->base = (ElemType *)malloc(MAXSIZE*sizeof(ElemType));
    if(!s->base)
    {
        printf("内存分配失败！\n");
        exit(0);
    }
    s->top = s->base;
    s->StackSize = MAXSIZE;
} 

void Push(sqStack *s, ElemType e)
{
    if(s->top - s->base == s->StackSize)
    {
        s->base = (ElemType *)realloc(s->base,(s->StackSize+INCREMENTSIZE)*sizeof(ElemType));
        if(!s->base)
        {
            printf("重新分配内存失败！\n");
            exit(0); 
        }
        s->top=s->base+s->StackSize;
        s->StackSize=s->StackSize+INCREMENTSIZE;
    }
    *(s->top) = e;
    s->top++;
}

void Pop(sqStack *s,ElemType *e)
{
    if(s->top == s->base)
    {
        return;
    }
    *e = *(--(s->top));
}

int StackLen(sqStack s)
{
    return (s.top - s.base);
}

int main(void)
{
    sqStack s;
    char c,e;
    
    InitStack(&s);
    printf("请输入中缀表达式\n");
    scanf("%c",&c);
    while(c !='#')
    {
        
        while(c>='0' && c<='9')
        {
            printf("%c",c);
            scanf("%c",&c);
            if(c<'0' || c>'9')
            {
                printf(" ");
            }
        }
        
        if(c==')')
        {
            Pop(&s,&e);
            while(e != '(')
            {
                printf("%c ",e);
                Pop(&s,&e);
            }
        }
        else if(c=='+' || c=='-')
        {
            if(!StackLen(s))
            {
                Push(&s,c);
            }
            else
            {
                do
                {
                    Pop(&s,&e);
                    if(e == '(')
                    {
                        Push(&s,e); //遇到左括号就弹走就ok 
                    }
                    else
                    {
                        printf("%c ",e);
                    }
                    
                }while(StackLen(s) && e!='(');
                Push(&s,c);
            }
        }
        else if(c=='/' || c=='*' || c=='(')
        {
            Push(&s,c);
        }
        else if(c == '#')
        {
            break;
        }
        else 
        {
            printf("数据输入错误啊！\n");
            return -1;
        }
        scanf("%c",&c);
    }
    while(StackLen(s))
    {
        Pop(&s,&e);
        printf("%c ",e);
    }
    return 0;
}