/*用棧實現計算器*/ 
/*經典的用來練習棧的題目，需要藉助逆波蘭表示式*/

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

#define MAXSIZE 64
#define OK 1
#define ERROR 0

typedef struct
{
    int data[MAXSIZE];
    int top;
}stacknode;

/*建立一個順序棧*/
stacknode * sqstack_create(void)
{
    stacknode * p;

    p = (stacknode *)malloc(sizeof
 
(*p));
    assert(p);      //分配空間後加上斷言是個好習慣
    p->top = -1;

    return p;
}

/*入棧操作*/
int sqstack_push(int n, stacknode * p)      
{
    if(p->top == (MAXSIZE - 1)) //棧滿
    {
        return ERROR;
    }
    p->data[++p->top] = n;

    return OK;
}

/*出棧操作*/
int sqstack_pop(int *dest, stacknode * p)
{
    if
 
(p->top == -1)    //棧空
    {
        return ERROR;
    }
    *dest = p->data[p->top--];

    return OK;
}

/*獲取棧頂值*/
int sqstack_top(int *dest, stacknode *p)        //const修飾指標*p，p指向的內容不可改變
{
    if(p->top == -1)    //棧空
    {
        return ERROR;
    }
    *dest = p->data[p->top];

    return
 
 OK;
}

/*列印棧中內容*/
int sqstack_print(stacknode *p)
{
    int n = p->top;

    if(n == -1) //棧空
    {
        return ERROR;
    }
    while(n)
    {
        printf(" %d ",p->data[n--]);
    }
    printf(" %d ",p->data[n]);
    printf("\n");
}

/*判斷棧是否為空*/
int sqstack_is_empty(stacknode *p)
{
    return (p->top == -1);
}

/*優先順序判斷函式*/
int get_priority(int ope)
{
    switch (ope)
    {
        case '+':
        case '-':return 1;
        case '*':
        case '/':return 2;
        case '(':return 0;
        default:return ERROR;
    }
}

/*提取兩個數和一個操作符進行計算，得到的結果再壓棧*/
void compute(stacknode *pnum,int ope)
{
    int num1,num2;
    int result;

    sqstack_pop(&num1,pnum);
    sqstack_pop(&num2,pnum);
    switch (ope)
    {
        case '+':   result = num1 + num2;
        case '-':   result = num1 - num2;
        case '*':   result = num1 * num2;
        case '/':   result = num1 / num2;
    }
    sqstack_push(result,pnum); 
}

/*進行優先順序計算*/
void deal_ope(stacknode *pnum,stacknode *pope,int ope)
{
    int old_ope;

    if(sqstack_is_empty(pope)||ope == '(')  //當空棧或符號為（ 時，將符號壓棧後返回 
    {
        sqstack_push(ope,pope);
        return;
    }
    sqstack_top(&old_ope,pope);     //得到棧頂元素 
    if(get_priority(ope)>get_priority(old_ope))             //比較優先順序，入參的符號優先順序大於棧頂元素時， 將符號壓棧後返回
    {
        sqstack_push(ope,pope);     
        return;
    }
    while(get_priority(ope)<=get_priority(old_ope))         
    {
        sqstack_pop(&old_ope,pope);
        compute(pnum,old_ope);      //以棧頂符號計算 後壓棧 
        if(sqstack_is_empty(pope))
        {
            break;
        }
        sqstack_top(&old_ope,pope);     
    }
    sqstack_push(ope,pope); //將新的操作符入棧
}

//處理括號 ，進行括號裡的高優先順序計算，之後將計算結果壓入數字棧，並且將括號丟棄 
void deal_bracket(stacknode *pnum,stacknode *pope)
{
    int old_ope;

    sqstack_top(&old_ope,pope);     //得到符號棧棧頂元素 
    while(old_ope != '(')           
    {
        sqstack_pop(&old_ope,pope);     //符號棧出棧 
        compute(pnum,old_ope);          //計算後將結果壓入數字棧 
        sqstack_top(&old_ope,pope);     //得到棧頂元素，進行下一次迴圈 
    }
    sqstack_pop(&old_ope,pope);     //將（ 出棧丟去 
}

int main()
{
    /*str為表示式陣列*/
    char str[MAXSIZE];
    printf("請輸入你要計算的表示式:\n");
    gets(str);

    int i = 0;
    int value = 0;   //數字的值
    int flag = 0;    
    int old_ope;

    stacknode *pnum,*pope;      // 定義兩個指向棧結構體的指標

    pnum = sqstack_create();  // 建立存放數字的棧

    pope = sqstack_create();  // 建立存放運算子號的棧

    /* 表示式字串解析函式,然後將高優先順序的符號/(*)進行計算重新入棧
       退出while大家的優先順序都一樣+-*/
    while (str[i] != '\0')
    {
        //獲取輸入的數字
        if (str[i] >= '0' && str[i] <= '9')//num
        {
            value = value * 10 + str[i] - '0';
            flag = 1;
        }
        else//ope
        {
            if (flag)
            {
                //flag = 1說明value裡面儲存了數字，將其入棧
                sqstack_push (value, pnum);
                //num標誌清零，value存放數字的變數清零
                flag = 0;
                value = 0;

            }
            if(str[i] == ')')
            {
                //如果是右括號，則
                deal_bracket(pnum,pope);    
            }
            else//+-*/(等情況 
            {
                deal_ope(pnum,pope,str[i]);
            }   
        }   
        i++;
    }

    //如果flag = 1.說明value裡面還有數值,將其入棧 

    if (flag)
    {
        sqstack_push(value,pnum);
    }
    //然後將符號與數字依次出棧計算。數字出棧計算完成之後回再次在compute中入棧
    while (!sqstack_is_empty(pope))
    {
        sqstack_pop(&old_ope,pope);
        compute(pnum,old_ope);
    }
    //取出數字棧最後剩下的數字，就是最後的答案
    sqstack_pop(&value,pnum);
    //列印結果
    printf("%s = %d\n",str,value);

    return 0;
}