如何查看向量中的内容？

Question

当我检查homework使用向量的内部值时cout，似乎只返回内部的值homework[0]。有人可以查看我的代码并让我知道我要去哪里了吗？

int main()
{
    cout << "Please enter midterm and final: " << endl;
    double midterm, gfinal;
    cin >> midterm >> gfinal;
    cout << "Enter all your homework grades, " << endl;

    double x;

    cin >> x;

    // initing a vector object named homework
    vector<double> homework;
    // show debug on the vector
    while (homework.size() != 3)
        homework.push_back(x);
    if (homework.size() == 0)
    {
        cout << endl << "You need to enter at least one number";
        return 1;
    }

    // vector before sorting
    // since cout << homework did not seem to work I could always just write a debug function to iterate over structures and print them to the console
    cout << homework[0] << endl; 
    cout << homework[1] << endl;
    cout << homework[2] << endl;

    // sort the vector here
    sort(homework.begin(), homework.end());

    // vector after sorting
    //cout << homework;
    cout << homework[0] << endl;
    cout << homework[1] << endl;
    cout << homework[2] << endl;


    int mid = homework.size() / 2;
    cout << "The below is mid" << endl;
    cout << mid << endl;

    double median;
    if (homework.size() % 2 == 0)
        median = (homework[mid - 1] + homework[mid]) / 2;
    else
        median = homework[mid];
    //streamsize prec = cout.precision(3);
    cout << "Your course grade is "
        << 0.2 * midterm + 0.4 * gfinal + 0.4 * median << endl;
    //cout.precision(prec);

    return 0;

}

这是引起我困惑的特定代码：

// vector before sorting
// since cout << homework did not seem to work I could always just write a debug function to iterate over structures and print them to the console

cout << homework[0] << endl; 
cout << homework[1] << endl;
cout << homework[2] << endl;

// sort the vector here
sort(homework.begin(), homework.end());

// vector after sorting
//cout << homework;
cout << homework[0] << endl;
cout << homework[1] << endl;
cout << homework[2] << endl;

程序启动时，它要求2个值，所以我插入了100100。然后它要求3个值，所以我使用80 90 100时cout，所有作业的位置在我期望80 90 100时都显示80。实际的程序有效最终的cout收益为92。

Answer 1

在您的代码中：

double x;

cin >> x; // <-- reading from cin only once

// initing a vector object named homework
vector<double> homework;
// show debug on the vector
while (homework.size() != 3)
    homework.push_back(x); // <- inserting same value three times

您只读取cin一次，即您正在读取一个值。然后，您将读取的值插入到vector中三次homework。因此，homework[0]，homework[1]和homework[2]包含相同的值。

考虑将其cin >> x放入while循环中以从中读取三次，cin而不是一次，即cin在循环的每次迭代中进行读取：

vector<double> homework;

while (homework.size() < 3) {
   double x;
   cin >> x;
   homework.push_back(x);
}