剛學完棧的時候寫的，主要鍛鍊下棧的C實現吧!

//棧用單鏈表來實現

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

struct Node1
{
    char a;
    struct Node1 *next;
};

struct Node2
{
    double a;
    struct Node2 *next;
};
typedef struct Node1 *Stack1;
typedef
 
 struct Node2 *Stack2;   
Stack1 CreakStack1()
{
    Stack1 S;
    S = (Stack1)malloc(sizeof(Node1));
    S->next = NULL;
    return S;
}

Stack2 CreakStack2()
{
    Stack2 S;
    S = (Stack2)malloc(sizeof(Node2));
    S->next = NULL;
    return S;
}



void Push1(char c, Stack1 S)
{
    Stack1 tmp;
    tmp = (Stack1)malloc
 
(sizeof(Node1));
    tmp->a = c;
    tmp->next = S->next;
    S->next = tmp;

}


void Push2(double c, Stack2 S)
{
    Stack2 tmp;
    tmp = (Stack2)malloc(sizeof(Node1));
    tmp->a = c;
    tmp->next = S->next;
    S->next = tmp;

}


void Pop1(Stack1 S)
{
    Stack1 tmp ;
    tmp = S->next;
    S->next = tmp->next;
    free
 
(tmp);
}


void Pop2(Stack2 S)
{
    Stack2 tmp;
    tmp = S->next;
    S->next = tmp->next;

}


char Top1(Stack1 S)
{
   return(S->next->a);
}

double Top2(Stack2 S)
{
    return(S->next->a);
}
bool Isempty1(Stack1 S)//這道題感覺沒什麼用！反正輸入合法！
{
    return S->next == NULL;
}
bool Isempty2(Stack2 S)
{
    return S->next == NULL;
}



char Prior[8][8] =
{ // 運算子優先順序表   
        // '+' '-' '*' '/' '(' ')' '#' '^'   
    /*'+'*/'>','>','<','<','<','>','>','<',
    /*'-'*/'>','>','<','<','<','>','>','<',
    /*'*'*/'>','>','>','>','<','>','>','<',
    /*'/'*/'>','>','>','>','<','>','>','<',
    /*'('*/'<','<','<','<','<','=',' ','<',
    /*')'*/'>','>','>','>',' ','>','>','>',
    /*'#'*/'<','<','<','<','<',' ','=','<',
    /*'^'*/'>','>','>','>','<','>','>','>'
};     

float Operate(float a, char c, float b)
{
    switch (c)
    {
    case '+':return a + b;
    case'-':return a - b;
    case'*':return a*b;
    case'/':return a / b;
    case'^':return pow(a, b);
    default:return 0;
    }
}

char OP[] = { "+-*/()#^" };           //把可能遇到的8個運算元預先存到一個數組中

int In(char a)                       //判斷字元是否為運算元
{
    int flag = 0;
    for (int i = 0; i < 8; i++)
        if (a == OP[i]) { flag = 1; continue; }
    return  flag;
}

int Ord(char a)                        //將運算元轉化為座標
{
    for (int i = 0; i < 8; i++)
        if (a == OP[i])return i;
}

char Precede(char a, char b)         //返回運算元的優先順序
{
    return(Prior[Ord(a)][Ord(b)]);
}

float Evaluate(char *Expression)
{
    Stack1 S1 = CreakStack1();
    Stack2 S2 = CreakStack2();
    Push1('#', S1);
    char cat[2] = "\0";
    char digit[20] = "";  //從表示式陣列中接受運算元部分
    strcat(Expression, "#");
    if (*Expression == '-');      //對第一個數是負數情況的處理；負數只會出現在字串的第一個或者左括號的下一個哦！！！
    Push2(0.0, S2);
    while (!(*Expression == '#'&&Top1(S1) == '#'))
    {
        if (!In(*Expression))//運算元
        {
            cat[0] = *Expression;
            strcat(digit, cat);
            Expression++;

            if (In(*Expression))
            {
                double Data = atof(digit);
                Push2(Data, S2);
                strcpy(digit, "\0");
            }

        }


        else     //操作符
        {
            if (*Expression == '(')                    //遇到負數的情況的處理；
            {
                if (*++Expression == '-')
                    Push2(0.0, S2);                     //壓入浮點數棧一個0；
                Expression--;                           //回到左括號。
             }
            switch (Precede(Top1(S1), *Expression))
            {
            case'<':
                Push1(*Expression, S1);
                Expression++;
                break;
            case'=':
                Pop1(S1);
                Expression++;
                break;
            case'>':
                char c = Top1(S1); Pop1(S1);
                double a = Top2(S2); Pop2(S2);
                double b = Top2(S2); Pop2(S2);
                Push2(Operate(b, c, a), S2);
                break;
            }//switch
        }//else
    }//while
    return(Top2(S2));


}


int main()
{
    char s[200];
    puts("請輸入表示式（括號在英文狀態下輸入）");
    scanf("%s", s);
    puts("該表示式的值為");
    printf("%f\n\n", Evaluate(s));
    system("pause");


}