为什么我在 C++ 的模板中遇到所有这些错误？

Question

这里是错误列表

错误：

 ||=== Build file: "no target" in "no project" (compiler: unknown) ===|
  F:\C Programs\TemplateClass.cpp|39|error: invalid use of non-static data member 'arraylist<x>::cap'| F:\C
  Programs\TemplateClass.cpp|11|note: declared here| F:\C
  Programs\TemplateClass.cpp||In instantiation of 'void arraylist<x>::fill() [with x = int]':| F:\C
  Programs\TemplateClass.cpp|65|required from here| F:\C
  Programs\TemplateClass.cpp|29|error: no match for 'operator>>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'int*')| c:\mingw\lib\gcc\mingw32\9.2.0\include\c++\istream|168|note:
  candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]' <near match>| c:\mingw\lib\gcc\mingw32\9.2.0\include\c++\istream|168|note:  
  conversion of argument 1 would be ill-formed:| F:\C
  Programs\TemplateClass.cpp|29|error: cannot bind non-const lvalue reference of type 'bool&' to an rvalue of type 'bool'

//code

#include <iostream>
using namespace std;
#include <conio.h>

template <class x>
class arraylist {
private:
    x* ptr;
    int cap, I;

public:
    arraylist(int cap)
    {
        ptr = new x[cap];
    }
    arraylist() //default constructor
    {
    }

    void fill()
    {
        cout << "Enter " << cap << " Elements :-\n";

        for (i = 0; i < cap; i++) {
            cout << "Enter " << i + 1 << " Element : ";
            cin >> ptr + i;
            cout << endl;
        }
    }

    void replace(int index, x value) //error message
    {
        *(ptr) + index = value;
    }

    void popdata(int index = cap - 1) //error message
    {
        delete (ptr + index);
    }

    void showdata(int index)
    {
        cout << "The data at index " << index << " is " << *(ptr + index);
    }

    void showlist()
    {

        for (i = 0; i < cap; i++) {
            cout << ptr + i << endl;
        }
    }
};

int main()
{
    arraylist<int> a1;

    a1 = 10;
    a1.fill();
    a1.showlist();
    a1.replace(2, 87);
    a1.showlist();
    a1.popdata(9);
    a1.showlist();
    getch();

    return 1;
}

Answer 1

首先停止使用这个：

#include <conio.h>

你拥有它的唯一原因是你可以使用：

getch();

您可以将其更改为要求使用具有相同效果的输入：

#include <iostream>
...

std::cout << "Please hit return to exit application\n";
std::cin.get();

---

请停止使用：

using namespace std;

是的，我知道必须在几件事前添加std::，但从长远来看，这会让您的生活更轻松。

---

错误：

 // You have not specified the type of i
 for (i = 0; i < cap; i++) {

C++ 中的所有变量都需要一个类型。添加这样的类型：

 // Note: There are two places to fix this.
 for (int i = 0; i < cap; i++) {

---

您访问数组成员的语法略有偏差：

 cin >> ptr + i;
 ...
 *(ptr) + index = value;

将这些更改为：

cin >> ptr[i];
...
ptr[index] = value;

---

void popdata(int index = cap - 1)
                      ^^^^^^^^^^ this part is not valid
                                 outside the class (where this is being called)
                                 you don't have accesses to the members.

为了让它发挥作用，暂时去掉那部分。

void popdata(int index)