c++ - 使用vector时出错:what():vector::_ M_range_check

Question

我是一名初学者程序员，并且正在尝试编写一个程序，询问用户以下内容:

P-打印数字

A-添加数字

M-显示数字的平均值

S-显示最小数字

L-显示最大数字

Q-退出

用户必须键入这些字母(无论是小写还是大写)才能使用它。目的是仅使用 vector 创建数字列表并执行上述操作

例如，如果我键入p，它应该显示列表为空(如果列表中没有数字)或以以下格式显示数字:[1 2 3]

在此处将相同格式应用于其他选择

这是我自己编写的代码:

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    int Count {1};
    char selection {};
    int Numbers {};
    double Sum {0};
    double Average {};
    int Minimum {};
    int Maximum {};
    vector <int> list;
    do {
        cout << "P - Print Numbers" << endl;
        cout << "A - Add Numbers" << endl;
        cout << "M - Display The Mean Of The Numbers" << endl;
        cout << "S - Display The Smallest Number" << endl;
        cout << "L - Display The Largest Number" << endl;
        cout << "Q - Quit" << endl;
        cout << "\nEnter Your Choice: ";
        cin >> selection;
        switch(selection){
            case 'P':
            case 'p':
                if(list.size() == 0){
                    cout << "\n[] - The List Is Empty" << endl;
                } else{
                    cout << "\n[ ";
                    for(size_t i{0}; i<=list.size(); ++i)
                        cout << list.at(i) << " ";
                    cout << "]" << endl;
                }
                break;
            case 'a':
            case 'A':
                cout << "\nEnter Your Number: ";
                cin >> Numbers;
                if (Count == 1){
                    Maximum = Numbers;
                    Minimum = Numbers;
                }
                if (Numbers > Maximum)
                    Maximum = Numbers;
                if (Numbers < Minimum)
                    Minimum = Numbers;
                list.push_back(Numbers);
                cout << "Added " << Numbers << endl;
                Count += 1;
                break;
            case 'm':
            case 'M':
                if (list.size() == 0)
                    cout << "Unable To Calculate The Mean - No Data" << endl;
                else {
                for (size_t j{0}; j<=list.size(); ++j){
                    Sum += list.at(j);
                    Average = Sum / list.size();
                }
                cout << "\nThe Mean Is : " << Average << endl;
                }
                break;
            case 's':
            case 'S':
                if (list.size() == 0)
                    cout << "Unable To Determine The Smallest Number - List Is Empty" << endl;
                else
                    cout << "\nThe smallest number is : " << Minimum << endl;
                break;
            case 'l':
            case 'L':
                 if (list.size() == 0)
                    cout << "Unable To Determine The Largest Number - List Is Empty" << endl;
                else
                    cout << "\nThe Largest number is : " << Maximum << endl;
                break;
            case 'q':
            case 'Q':
                cout << "Goodbye!!" << endl;
                break;
            default:
                cout << "Unknown Selection, Please Try Again!" << endl;
        }
    } while (selection != 'q' && selection != 'Q');
    return 0;
}

问题是我可以成功添加号码，但是当我尝试打印列表时我得到以下信息:

    terminate called after throwing an instance of 'std::out_of_range'
  what():  vector::_M_range_check: __n (which is 1) >= this->size() (which is 1)

当然，现在我已经说过我可以在没有任何错误或警告的情况下运行它了。我还尝试将 size_t更改为 int，但是我收到了两个警告...并且我也使用 .push_back()作为 vector ，因此我没有空 vector ...

任何帮助都会很棒..谢谢:)

Answer 1

for (size_t j{0}; j<=list.size(); ++j)中的小于或等于比较不正确。

考虑最后一次迭代... j将等于list.size()。

相反，对列表元素的规范迭代是:

    for (size_t i{0}; i < list.size(); ++i)
        std::cout << list[i] << " ";

如上所示，您可以将 list.at(i)更改为 list[i]，因为您知道索引将是有效的。

最后，我建议不要对 vector 使用名称 list，因为这是C++标准库中的链接列表类型的名称。