利用栈求表达式的值

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cctype>
#include <ctime>

using namespace std;

template <class T>
class stack
{
    private:
        int sum=0;
        struct node{
        T data;struct node *link;
        };
    public:
        struct node *ttop=NULL;
        stack(){ttop=NULL;sum=0;}
        ~stack()
        {
            struct node *temp;
            while (ttop)
            {
                temp=ttop;ttop=ttop->link;
                delete temp;
            }
        }
    inline bool empty()
    {
        if (ttop)return false;
        else return true;
    }
    bool push(const T item)
    {
        struct node *temp=new node;
        if (temp){sum++;temp->data=item;temp->link=ttop;
        ttop=temp;return true;}
        else return false;
    }
    bool pop(void)
    {
        if (empty())return false;
        else {
            sum--;
            struct node *temp;
            temp=ttop;
            ttop=ttop->link;
            delete temp;return true;
        }
    }
T top(void)
        {
            if (sum>0)
            return ttop->data;
            else return 0x7fffffff;
        }
int size(void){return sum;}
};

class expression{
private:int Numlen(char *s)
{
    int i=0;int f=0;
    while (s[i]=='.'||isdigit(s[i])){
        if (s[i]=='.')f++;
        i++;}
    if (f>1)return -1;
    return i;
    }
double Read(char *s)
{
    double num;
    sscanf(s,"%lf",&num);
    return num;
    }
public:char s[1000];
double Calc(void)
{
    double a,b,sum;
    int l;
    stack <double> Num;
    stack <char> Op;
    while (!Num.empty())Num.pop();
    while (!Op.empty())Op.pop();
    if (s[0]=='+'||s[0]=='-')Num.push(0);
    int flag=0;
    while (s[flag]!='\0')
    {
        switch(char t=s[flag])
        {
            case '(':Op.push('(');flag++;break;
            case ')':
                sum=0;
                while (Op.top()!='('){
                a=Num.top();Num.pop();
                char c=Op.top();Op.pop();
                if (c=='+')sum+=a;
                else if (c=='-')sum-=a;
                }
                Op.pop();
                b=Num.top()+sum;Num.pop();Num.push(b);
                flag++;
                if (Op.top()=='*'||Op.top()=='/')
                {
                    a=Num.top();Num.pop();
                    if (Op.top()=='*'){b=Num.top()*a;Num.pop();Num.push(b);}
                    else {b=Num.top()/a;Num.pop();Num.push(b);}
                    Op.pop();
                }
                break;
            case '+':case '-':
                flag++;Op.push(t);
                break;
            case '*':case '/':flag++;
                if (s[flag]!='('){
                a=Read(s+flag);
                int l=Numlen(s+flag);flag+=l;
                if (t=='*'){b=Num.top()*a;Num.pop();Num.push(b);}
                else if (t=='/'){b=Num.top()/a;Num.pop();Num.push(b);}
                }
                else Op.push(t);
                break;
            default:{
                a=Read(s+flag);Num.push(a);
                l=Numlen(s+flag);flag+=l;
                }break;
            }
        }
    sum=0;
    while (!Op.empty())
    {
    if (Op.top()=='+')sum+=Num.top();
    else if (Op.top()=='-')sum-=Num.top();
    Num.pop();Op.pop();
    }
    sum+=Num.top();
    return sum;
}
};

class Main_code{
private:
class expression s[100];
int sum=0,sumt=0,sumc=0;
void cl(void)
{
    system("pause");
    system("cls");
}
void save(void)
{
    system("cls");
    puts("正在保存记录");
    freopen("记录.txt","w",stdout);
    printf("%d\n%d\n",sum,sumc);
    fclose(stdout);freopen("con","w",stdout);
    puts("保存成功");
    system("pause");
}

void ex(void)
{
    sum++;
    int num=rand()%sumt;
    puts(s[num].s);
    double Ca=s[num].Calc();
    double Ya;scanf("%lf",&Ya);
    if (Ya==Ca){sumc++;puts("Good job!答对了");}
    else {puts("孩子,这个题你也能错?");printf("正确答案应该是%g!\n",Ca);}
}

void bl(void)
{
    if (sum==0)puts("你还没有做过题！");
    else {
        puts(" ------------------ ");
        printf("|你一共做过%4d道题|\n|正确的共有%4d道题|\n|正确率应为  %5.2lf%%|\n",sum,sumc,(double)sumc/(double)sum);
        puts(" ------------------ ");
    }

}
public:bool Initt(void)
{
    srand((unsigned)time( NULL));
    if(freopen("题库.txt","r",stdin)==NULL){puts("未找到题库！");system("pause");return 0;
    }
    printf("正在载入题库");
    while (gets(s[sumt].s)){if(s[sumt].s[0]!='\0')sumt++;putchar('.');}
    putchar('\n');
    puts("正在载入记录");
    fclose(stdin);
    if(freopen("记录.txt","r",stdin)!=NULL){
    if(scanf("%d%d",&sum,&sumc)==EOF){sum=0,sumc=0;puts("记录为空!");}
    }
    else puts("未找到记录");
    fclose(stdin);freopen("CON","r",stdin);
    puts("载入完毕");
    system("pause");system("cls");return 1;
    }
bool Menu(void)
{
    puts("      小学算术系统      ");
        puts("************************");
        puts("      (1).题目练习      ");
        puts("      (2).历史回顾      ");
        puts("      (3).退出          ");
        puts("************************");
        printf("请输入你的选择:(1~3):");
        int C;scanf("%d",&C);
        switch (C)
        {
            case 1:{printf("请完成下面5道计算题:\n");for (int c=0;c<5;c++){
                puts("-------------------");
                printf("(%d).",c+1);ex();}
                puts("-------------------");
                break;
                }
            case 2:{bl();break;}
            case 3:{save();return 1;}
            default:{puts("选择无效!");
            break;}
        }cl();return 0;
    }
};

int main(void)
{
    class Main_code One;
    if(One.Initt()==0)return 0;
    while (true)
    {
        if(One.Menu())break;
    }
    return 0;
}