如何聲明一個在編譯時不知道大小的數組？

Question

我正在嘗試實現random_function() ，它輸出范圍內（用戶輸入）內的隨機數的數量，以及count_function()來計算用戶想要在輸出的隨機數中查找的值。 我將隨機數保存在一個名為randomlist[]的數組中，以便它可以用於計算輸出隨機數的值。 但是，我不能在 header 文件中聲明一個沒有固定大小的數組，並在 count_function.cpp 中定義它的大小。 所以我不能在count_function()中使用randomlist[]而不重新定義它（這是沒有意義的......）。
有沒有辦法在 header 文件中聲明數組而不定義其大小？

這是源代碼：

header 文件：

#pragma once

using namespace std;

class Rand
{
  public:
    // Rand();
    int range,min,max;
    char key;
    void Random_function();
    void Count_function();
    // randomlist[]; something like this, which that is not possible in c++
};

這是隨機函數.cpp：

#include <iostream>
#include "random_function.hpp"


using namespace std;

void Rand::Random_function()
{
    beginning:
    
    cout << "Enter amount of numbers to generate: ";
    cin >> range;
    
    if (range<=0 || cin.fail())
    {
        cout <<"Error! Please enter valid number and try again! "<<endl;
        goto beginning;
    }

    else
    {
     reenter:

        
        cout << "Enter minimum boundary: ";
        cin >> min;
        cout << "Enter maximum boundary: ";
        cin >> max;
        cout << "\n";
        
        srand((unsigned)time(NULL));
    
        if(max<min || cin.fail())
            {
                cout << "\nError! Please enter the valid value and try again! " << endl;
                goto reenter;
            }
        
        else
            {
              int randomlist[range]; //I defined the size of the randomlist here but I want to use this outside of the random_fucntion() as well. 
                
              for(int i=0 ; i < range; i++)
              {
                  
                randomlist[i] = min + (rand() % static_cast<int>(max - min + 1));
              
                cout <<i+1<<". "<< randomlist[i] <<endl;
              
                
            }
    
    }
        
        cout <<"\n"<< "Total random numbers generated: " << range<< endl;
  
    
      cout <<"Do you want to continue? y/n"<<endl;
      cin >> key;
    
    if(key=='y')
    {
            Count_function();
        
            cout <<"Do you want to restart? y/n"<<endl;
            cin >> key;
            if(key=='y')
            {
                goto beginning;
            }
            else
            {
                exit(0);
            }

    }
    
    else
    {
        cout <<"Do you want to restart? y/n"<<endl;
        cin >> key;
        
        if(key=='y')
        {
                goto beginning;
        }
            
        else
        {
            exit(0);
        }
     
    }
  }   
    
}


void Rand::Count_function()
{
    
    int n,count=0;
    
    reenter2:
    
    cout<<"Enter the value to count for: ";
    cin>>n;
    
if(cin.fail())
{
    cout<<"Please enter valid value to count for"<<endl;
    goto reenter2;
}
    
else
{
    
    for(int i=0 ; i <range; i++)
    {
        if(randomlist[i]==n)
        {
            count++;
        }
    }
}
    cout <<"The number of '"<<n<<"'s in the given list is: "<< count <<endl;
}

主要的：

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <random>
#include "random_function.hpp"

using namespace std;

int main()
{
    Rand call;
    call.Random_function();
}

Answer 1

當您想使用數組，但在編譯時無法知道大小時，C++ 中普遍接受的方法是使用std::vector 。