堆栈c ++的打印功能

Question

I am trying to print the contents of my stack. here is my code: Stack.h

#pragma once
#include <iostream>

using std::cout;                            // specific commands from namespace std
using std::cin;
using std::endl;

typedef unsigned long Item;

class Stack
{
private:
    enum { MAX = 10 };  // MAX elements in this stack
    Item items[MAX];    // holds stack items
    int top;            // index for the top stack item
    int first, last;

public:
    Stack();
    Stack(int, int);
    ~Stack();
    void printCurr() const;
    void printCurrReverse() const;
    bool isempty() const;
    bool isfull() const;
    // return false if stack already full
    bool push(const Item& item);    // add item to stack
                                    // return false if stack already empty
    bool pop(Item& item);

};

stack.cpp

#pragma once
#include "Stack.h"
#include <iostream>
using std::cout;
using std::cin;
using std::endl;


Stack::Stack()
{
    for (int i = 0; i < MAX; i++) //for loop that sets the initial array values to null
    {
        items[i] = 0;
    }   
    top = 0;
}


Stack::Stack(int first , int last)
{

    if (top <= 4)
    {
        for (int i = 0; i <= 4; i++)
        {
            this -> items[i] = first;
        }
    }

    if (top >= 5 && top <= MAX)
    {
        for (int i = 0; i <= MAX; i++)
        {
            this -> items[i] = last;
        }
    }

}

Stack::~Stack()
{
}


void Stack::printCurr() const
{
    int index = 0;
    for (int i = index; i < MAX; i++)
    {
        cout << index + i;
    }
}

void Stack::printCurrReverse() const
{
    int index = top - 1;
    for (int i = index; i >= 0; i++)
    {
        cout << index + i;
    }
}



bool Stack::isempty() const
{
    return top == 0;
}

bool Stack::isfull() const
{
    return top == MAX;
}

bool Stack::push(const Item& item)
{
    if (top < MAX)
    {
        items[top++] = item;
        return true;
    }
    else
        return false;
}

bool Stack::pop(Item& item)
{
    if (top > 0)
    {
        item = items[--top];
        return true;
    }
    else
        return false;
}

main.cpp

#include <iostream>
#include <sstream>
#include "Stack.h"


using namespace std;

int main()
{

    Stack st1;

    char ch;
    unsigned long sc;
    cout << "Please Enter 'A' to Add A Score You Wish To Record, \n"
        << "Press R To Record A Score, V To View Recorded Scores & Q to Quit" << endl;
    while (cin >> ch && toupper(ch) != 'Q')
    {
        while (cin.get() != '\n')
            continue;
        if (!isalpha(ch))
        {
            cout << '\a';
            continue;
        }
        switch (ch)
        {
        case 'a':
        case 'A': cout << "Enter A Score To Add: ";
            cin >> sc;
            if (st1.isfull())
                cout << "stack already full\n";
            else
                st1.push(sc);
            break;
        case 'R':
        case 'r': if (st1.isempty())
            cout << "stack already empty\n";
                  else {
                      st1.pop(sc);
                      cout << "Score #" << sc << " popped\n";
                  }
                  break;
        case 'V':
        case 'v':

            cout << "Your Recorded Scores are : " << st1.printCurr() << endl;
            cout << "Your Recorded Scores In Reverse Order Are : " << st1.printCurrReverse() << endl;

            cout << "Please enter A to add a purchase order,\n"
                << "P to process a PO, or Q to quit.\n";
        }

        system("pause");
        return 0;
    }
}

my problem is the print functions. I am getting the following error

Error C2679 binary '<<': no operator found which takes a right-hand operand of type 'void' (or there is no acceptable conversion)
main.cpp 48

from what I understand this is happening because I am not overloading the << operator correctly.

I need the print function to be with out parameters and without a return value. What am I doing wrong?

Answer 1

Your print functions printCurr and printCurrReverse return void, and therefore cannot be used as parameter of std::cout (in your main ). Your functions already print it with cout.

You could let your function return string instead. Or remove them from the cout line.

The simplest way, put them out of the cout line:

cout << "Your Recorded Scores are : ";
st1.printCurr();
cout << "Your Recorded Scores In Reverse Order Are : "; 
st1.printCurrReverse();

Otherwise let your print functions return a string which you can create with stringstream for example:

std::string printCurrReverse() {
  stringstream strs;
  strs << " text "<< 33; //example
  return strs.str();
}

Answer 2

First of all this constructor

Stack::Stack(int first , int last)
{

    if (top <= 4)
    {
        for (int i = 0; i <= 4; i++)
        {
            this -> items[i] = first;
        }
    }

    if (top >= 5 && top <= MAX)
    {
        for (int i = 0; i <= MAX; i++)
        {
            this -> items[i] = last;
        }
    }

}

does not make sense and has undefined behaviour because data member top is not initialized. And it is not clear what you are trying to do.

Function printCurr also does not make sense

void Stack::printCurr() const
{
    int index = 0;
    for (int i = index; i < MAX; i++)
    {
        cout << index + i;
    }
}

It simply outputs natural numbers in the range [0, MAX - 1]

If you mean to output the values stored in the stack then the function can look the following way

void Stack::printCurr() const
{
    for ( int i = top; i != 0; )
    {
        cout << items[--i];
    }
}

Correspondingly function printCurrReverse can look like

void Stack::printCurrReverse() const
{
    for ( int i = 0; i != top ; i++)
    {
        cout << items[i];
    }
}

Else as the functions have return type void you may not use them like

cout << "Your Recorded Scores In Reverse Order Are : " << st1.printCurrReverse() << endl;

If you want to use them such a way then they should be defined like

std::ostream & Stack::printCurr( std::ostream &os = std::cout ) const
{
    for ( int i = top; i != 0; )
    {
        os << items[--i];
    }

    return os;
}

and

std::ostream & Stack::printCurrReverse( std::ostream &os = std::cout ) const
{
    for ( int i = 0; i != top ; i++)
    {
        os << items[i];
    }

    return os;
}