使用C ++在向量中设置开关

Question

我正在尝试学习C ++，但是我有些困惑。

我正在使用Geany和CentOS创建基本的成绩簿应用程序。

Geany在应用程序的for和cout行上显示红色的卷曲线。我觉得一切都使用了正确的语法，但出现“编译失败。”

我的来源出了什么问题？

#include <vector>
#include <string>
#include <iostream>

using namespace std;

int main(void){

    // Declaration of local variables for gradebook
    vector<int> gradeVector;
    char choice;
    bool menu = true;

    // User Menu
    while (menu){
        cout << "This is the gradebook menu\n";
        cout << "Please enter (a) to Show All Grades\n";
        cout << "Please enter (l) to Show Last Grade\n";
        cout << "Please enter (g) to Add Grade\n";
        cout << "Please type 0 to Exit.\n";
        cin >> choice;

        switch(choice){
            case 'a':
                for (i=0;i <= gradeVector.size(); i++)
                cout << "These are the grades entered: \n"<<gradeVector.at(i);
            break;
            case 'l':
                cout << "This was the last grade entered: \n" << gradeVector;
            break;
            case 'g':
                cout << "Please add a grade to the gradebook: \n" << cin >> gradeVector.push_back();
            break;
            case 0:
                menu = false;
            break;
            default:
                cout << "Please ONLY use lower-case a, l, g, or 0 as your choice.\n"
        }
    }
    return (0);
}

Answer 1

您的代码中存在多个错误。首先，您忘记声明整数i。您尝试输出矢量，并且从您的文字中我收集到您只想要最后的成绩。输入应使用push_back进行，但应首先将其读入临时变量。更正此问题并更改一些通用代码将使您成为代码：

#include <vector>
#include <string>
#include <iostream>

using namespace std;

int main(void){

    // Declaration of local variables for gradebook
    vector<int> gradeVector;
    char choice;
    bool menu = true;

    // User Menu
    while (menu){
        cout << "This is the gradebook menu\n";
        cout << "Please enter (a) to Show All Grades\n";
        cout << "Please enter (l) to Show Last Grade\n";
        cout << "Please enter (g) to Add Grade\n";
        cout << "Please type 0 to Exit.\n";
        cin >> choice;

        switch(choice){
            case 'a':
                cout << "These are the grades entered: \n"
                for (int i=0 ;i < gradeVector.size(); i++)
                    cout << gradeVector[i] << " ";
            break;
            case 'l':
                cout << "This was the last grade entered: \n" << gradeVector[gradeVector.size()-1];
            break;
            case 'g':
                cout << "Please add a grade to the gradebook: \n";
                int input;
                cin >> input;
                gradeVector.push_back(input);
            break;
            case 0:
                menu = false;
            break;
            default:
                cout << "Please ONLY use lower-case a, l, g, or 0 as your choice.\n";
        }

     }

    return (0);
}

Answer 2

对于一个，您的for循环语法是错误的。

for (i=0;i <= gradeVector.size(); i++)

每次都会给您一个segmentation fault，应该是

for (i=0;i < gradeVector.size(); i++)

因此，您不会访问超出范围的内存。请记住，计数从0开始，并且您访问的内存不能超过分配的内存。

您的编译错误在这里：

cout << "This was the last grade entered: \n" << gradeVector;

您不能引用这样的向量；您必须指出一个特定的元素。如果要删除向量中的所有元素，请使用for循环。