Question

我正在尝试打印堆栈的内容。这是我的代码： 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;
}

的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;
    }
}

我的问题是打印功能。我收到以下错误

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

根据我的理解，这种情况正在发生，因为我没有正确地重载<<运算符。

我需要打印功能不带参数且没有返回值。我做错了什么？

Answer 1

您的打印功能copy和printCurr返回无效，因此无法用作printCurrReverse的参数（在std::cout中）。你的功能已经用cout打印出来。

您可以让函数返回字符串。或者从main行中删除它们。

最简单的方法是将它们排除在cout线之外：

cout

否则，让您的打印功能返回cout << "Your Recorded Scores are : "; st1.printCurr(); cout << "Your Recorded Scores In Reverse Order Are : "; st1.printCurrReverse();，您可以使用string创建该代码：

stringstream

Answer 2

首先是这个构造函数

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;
        }
    }

}

没有意义并且具有未定义的行为，因为数据成员top未初始化。目前尚不清楚你要做什么。

功能printCurr也没有意义

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

它只输出[0, MAX - 1]

范围内的自然数

如果您要输出存储在堆栈中的值，则该函数可以按以下方式显示

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

相应的函数printCurrReverse可能看起来像

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

否则函数的返回类型为void，您可能不会像

那样使用它们

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

如果你想以这种方式使用它们，那么它们应该被定义为

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

    return os;
}

和

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

    return os;
}

stack c ++

2 个答案: