C++实现数据结构作业——表达式求值

　　

    /*用到了class, template,析构函数，构造函数，C++菜鸟一只，大牛无视。各种bug，待修改。。。*/
//My Code:

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>

using namespace std;

const int N = 256;
char map[N][N];

template <class T>

class Node{
public:
    T data;
    Node * next;
    Node(const T &e, Node<T> *t){
        data = e;
        next = t;
    }
};

template <class T>

class LinkStack{
private:

    Node<T> * top;
    void init(){
        top = NULL;
    }
public:
    void Clear(){
        T tmp;
        while(!Empty())
            Pop(tmp);
    }
    LinkStack(){
        init();
    }
    virtual ~LinkStack(){
        Clear();
    }
    int Length() const
    {
        int count = 0;
        for(Node<T> * i = top; i != NULL; i = i->next){
            count++;
        }
        return count;
    }
    bool Empty() const{
        return top == NULL;
    }
    int Push(const T &e){
        Node<T> * new_top = new Node<T>(e, top);
        if(new_top == NULL)
            return 0;
        else{
            top = new_top;
            return 1;
        }
    }
    T GetTop(T &e) const{
        if(Empty()){
            return 0;
        } else {
            e = top->data;
            return e;
        }
    }
    int Pop(T &e){
        if(Empty()){
            return 0;
        } else {
            Node<T> * old_top = top;
            e = old_top->data;
            top = old_top->next;
            delete old_top;
            return 1;
        }
    }

};

char c[10];
int i;

void get_in(){

    memset(c, 0, sizeof(c)); i = 0;
    while(cin.get(c[i++])){
        if(c[i-1] == ' ')
            break;
    }
}

void inite(){
    map['+']['+'] = map['+']['-'] = map['+'][')'] = map['+']['#'] = '>';map['+']['*'] = map['+']['/'] = map['+']['('] = '<';
    map['-']['+'] = map['-']['-'] = map['-'][')'] = map['-']['#'] = '>';map['-']['*'] = map['-']['/'] = map['-']['('] = '<';
    map['*']['+'] = map['*']['-'] = map['*']['*'] = map['*']['/'] = map['*'][')'] = map['*']['#'] = '>'; map['*']['('] = '<';
    map['/']['+'] = map['/']['-'] = map['/']['*'] = map['/']['/'] = map['/'][')'] = map['/']['#'] = '>'; map['/']['('] = '<';
    map[')']['+'] = map[')']['-'] = map[')']['*'] = map[')']['/'] = map[')'][')'] = map[')']['#'] = '>';
    map['(']['+'] = map['(']['-'] = map['(']['*'] = map['(']['/'] = map['(']['('] = '<'; map['('][')'] = '=';
    map['#']['+'] = map['#']['-'] = map['#']['*'] = map['#']['/'] = map['#']['('] = '<'; map['#']['#'] = '=';
}

char Precede(char a, char b){
    return map[(int)a][(int)b];
}

int Oprate(int a, char t, int b){
    int x;
    switch (t){
        case '+':
            x = a + b; break;
        case '-':
            x = a - b; break;
        case '*':
            x =  a * b; break;
        case '/':
            x =  a / b; break;
    }
    return x;
}

int In(char c){
    if(c == '+' || c == '-' || c == '*' || c == '/' || c == '(' || c == ')' || c == '#')
        return 1;
    return 0;
}

int solve(){
    LinkStack<int> opnd;
    LinkStack<char>    optr; optr.Push('#');
    char e, th;
    int f, b, a;
    get_in();
    while(c[0] != '#' || (optr.GetTop(e) !='#')){
        if(!In(c[0])){
            f = 0;
            for(int j = 0; j < i-1; j++){
                f += (c[j]-'0') * pow(10.0, i-2-j);
            }
            opnd.Push(f);
            get_in();
        } else {
            switch (Precede(optr.GetTop(e), c[0])){
                case '<':
                    optr.Push(c[0]); get_in();
                    break;
                case '=':
                    optr.Pop(e); get_in();
                    //cout << optr.GetTop(e) << endl;
                    break;
                case '>':
                    optr.Pop(th);
                    opnd.Pop(b); opnd.Pop(a);
                    opnd.Push(Oprate(a, th, b));
                    //cout << a << " " << th << " " << b << endl;
                    //cout << opnd.GetTop(f) << endl;
                    break;
            }
        }
    }
    return opnd.GetTop(f);

}
int main(){
    //freopen("data.in", "r", stdin);
    inite();
    cout << "Please input the Expresssion : " << endl;
    cout << solve() << endl;
    return 0;
}