基于堆栈的回文检查器

Question

i have a problem with my program. It should be program that recognize palindome through the stack. Everything works great, only thing that don't work is printing stacks(original and reversed) after the funcion is done. Here is my entire code, and the problem is at case d and e:

#include <iostream>

using namespace std;


const int MAXSTACK = 21;
class stack {
private:
    int  stop;  
    char stk[MAXSTACK];
public:
    stack();
    ~stack();
    stack(const stack& s);
    void push(const char c);
    char pop();
    char top(void);
    int  emptystack(void);
    int  fullstack(void);
    void stack_print(void);
    int stack::create(void);
};
stack::stack()
{
    stop = 0;
}
stack::~stack() { }  
stack::stack(const stack& s)
{
    stop = s.stop;
    strcpy(stk,s.stk);
}
void stack::push(const char c)
{
    stk[stop++] = c;
}
char stack::pop()
{
    return stop--;
}
char stack::top(void)
{
    return stk[stop - 1];
}
int  stack::emptystack(void)
{
    return !stop; 
}
int  stack::fullstack(void)
{
    return stop == MAXSTACK;
}
void stack::stack_print(void)
{
    for (int i=0; i<stop; i++)
        cout<<stk[i];
    cout<<endl;
}
int  stack::create(void)
{
    return !stop; 
}
char menu()
{

    char volba;

    cout<<"\n";
    cout<<" **********.\n";
    cout<<"\n";
    cout<<" a ... make new containers\n";
    cout<<" b ... delete content\n";
    cout<<" c ... enter string\n";
    cout<<" d ... print on screen first stack\n";
    cout<<" e ...  print on screen first stack\n";
    cout<<" f ... is it palindrom\n";
    cout<<" x ... exit\n";
    cout<<"\n your choice : ";

    cin >>  volba;
    return volba;
}
int main() {
    char  palindrome[MAXSTACK]; 
    char volba;
    stack original,reversed;
    int   stackitems = 0,i;
    //cin.getline(palindrome,MAXSTACK);
    do{
        volba = menu();
        switch (volba)
        {
        case'a':
            {
                original.create();
                reversed.create();
                cout<<"done'";
                break;
            }
        case'b':
            {
            original.emptystack();
            reversed.emptystack();
            cout<<"empty";
            break;
            }
        case'c':
            {
                cout<<"enter your string"<<endl;
            cin.get();
            //cin.get();
            cin.getline(palindrome,MAXSTACK);
    for(int o = 0; o < strlen(palindrome); o++)

        if (isalpha(palindrome[o]))
        {
            original.push(tolower(palindrome[o]));
            stackitems++;                           
        }
            original.stack_print();

        break;
            }
        case'd':
            {
                original.~stack();
                for(int g = 0; g < strlen(palindrome); g++)
                original.push(tolower(palindrome[g]));
                original.stack_print();
            }
            /*//cin.getline(palindrome,MAXSTACK);
    for(int g = 0; g < strlen(palindrome); g++)

        if (isalpha(palindrome[g]))
        {
            original.push(tolower(palindrome[g]));
            stackitems++;                           
        }

            }
            original.stack_print();*/
            break;


        /*{
                cout<<"original: ";
        original.stack_print();
                break;
            }*/
            break;
        case'e':
            {
            cout<<"reversed:"<<endl;
            for( i = 0; i < stackitems; i++) {
            reversed.push(original.top());
            original.pop();
        }
        reversed.stack_print();
            }
            break;

        case'f':
            {
            for( i = 0; i < stackitems / 2; i++) {
            reversed.push(original.top());
            original.pop();
        }


        if (stackitems % 2)
            original.pop();

        while (!original.emptystack()) {
            if (original.top() != reversed.top()) break;
            original.pop(); reversed.pop();
        }
        if (original.emptystack())
            cout << "it is palindrom\n";
        else
            cout << "not palindrom\n";

        break;

            }
        default:cout<<"!??!";


        }
    } while(volba!='x');
}

Answer 1

You've explicitly called your stack's destructor. There is almost never a good reason to do this. If the stack is a local ("on the stack", hee hee), the compile will do it for you. If it's on the heap, created with new , call delete on it, which will cause the compiler to call the destructor.

    case'd':
            {
                    original.~stack();

Answer 2

您已评论回文读物:)

//cin.getline(palindrome,MAXSTACK);

Answer 3

There are a few things I would like to respond with. First, I think GMan, tpdi, and Vinay all have good points. This FAQ explains why calling the destructor on a local variable is a bad idea.

I realize this is just a simple homework problem and you are probably just trying to keep your stack class lightweight, but you might consider using a container class instead of an array of characters in your stack class.

Next, I'm not sure your emptystack and create functions are doing what you think they are doing. When you declare your original and reversed stack classes in the main program the memory is allocated for your internal character array. It's not really necessary in this case to have a create function. Perhaps if you were allocating memory on the heap for your character array, you would put that code into the create function (if you chose to leave it out of the constructor for some reason), but that's not the case here.

Similarly, emptystack isn't really doing anything. It would be better to have empty stack set the stop member variable to 0. At least that way the stack would appear to be empty the next time someone tried to use it.

There's a lot more that could be said about this class, but it might be better if you tried some of the suggestions here like using the std::stack and debugging. This is, after all, your homework assignment: it will help you a lot more in the future if you find the solution yourself!