我的代码有什么问题（c ++初学者）？ [关闭]答案

【问题标题】：What's wrong with my code (c++ beginner)? [closed]我的代码有什么问题（c ++初学者）？ [关闭]
【发布时间】：2018-02-04 02:32:42
【问题描述】：

我是新来的编码和初学者 C++ 课程，我真的不确定我的代码有什么问题。我把东西搬来搬去无济于事。该程序旨在询问用户字母等级以及它的 +、- 或无符号（例如 A+、A-、A）。我必须使用 switch 和 if 语句，但我不确定我的逻辑在哪里失败。

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

int main()
{
char sign, letterGrade;
string gradeRange;

cout << "Enter a letter grade: ";
cin >> letterGrade;

cout << "Enter a sign (+ or -) if applicable; otherwise, enter 'x': ";
cin >> sign;

switch (letterGrade) {
case 'A': {
        if (sign == '+' || sign == 'x') {
            gradeRange = "greater than 93%";
        }
        else if (sign == '-') {
            gradeRange = "greater than or equal to 90%, but less than 93%.";
        }
        break;
    }
    case 'B': {
        if (sign == '+') {
            gradeRange = "greater than or equal to 87%, but less than 90%.";
        }
        else if (sign == 'x') {
            gradeRange = "greater than or equal to 83%, but less than 87%.";
        }
        else if (sign == '-') {
            gradeRange = "greater than or equal to 80%, but less than 83%.";
        }
        break;
    }
    case 'C': {
        if (sign == '+') {
            gradeRange = "greater than or equal to 77%, but less than 80%.";
        }
        else if (sign == 'x' || sign == '-') {
            gradeRange = "greater than or equal to 70%, but less than 77%.";
        }
        break;
    }
    case 'D': {
        if (sign == '+' || sign == '-' || sign == 'x') {
            gradeRange = "greater than or equal to 60%, but less than 70%.";
        }
        break;
    }
    case 'F': {
        if (sign == '+' || sign == 'x' || sign == '-') {
            gradeRange = "less than 60%.";
        }
        break;
    }
    default: {
        cout << "Oops, an error occured, please try again.";
    }
cout << "The student's letter grade range is " << gradeRange << endl;

}


return 0;

}

【问题讨论】：

代码到底有什么问题？
正确缩进你的代码，你会清楚地看到哪里出了问题。
你有最后的cout-statement inside switch-block，这意味着它被每个break-statement 跳过。
这个问题很快就会变得不愉快（即，它很可能会被否决）。要从中学习：总是检查阅读您的输入！例如if (std::cin >> letterGrade) { /* use the value */ } else { /* deal with the input error */ }.
您也可以清理您的代码，方法是在您的案例中为“A”、“B”和“C”不以“else-if”语句结尾。对于案例“D”和“F”，您也不需要“if”语句。试试看这个调整是否适合你。

标签： c++ c++11 debugging logic

【解决方案1】：

你有最终的 cout 语句在 switch-block，这意味着它被每个 break-statement 跳过。

【讨论】：

【解决方案2】：

#include <iostream>
#include <string>

using namespace std;

int main()
{
    char sign, letterGrade;
    string gradeRange;

    cout << "Enter a letter grade: ";
    cin >> letterGrade;

    cout << "Enter a sign (+ or -) if applicable; otherwise, enter 'x': ";
    cin >> sign;

    switch (letterGrade) {
    case 'A': 
            if (sign == '+' || sign == 'x') {
                gradeRange = "greater than 93%";
            }
            else if (sign == '-') {
                gradeRange = "greater than or equal to 90%, but less than 93%.";
            }
            break;

        case 'B': 
            if (sign == '+') {
                gradeRange = "greater than or equal to 87%, but less than 90%.";
            }
            else if (sign == 'x') {
                gradeRange = "greater than or equal to 83%, but less than 87%.";
            }
            else if (sign == '-') {
                gradeRange = "greater than or equal to 80%, but less than 83%.";
            }
            break;

        case 'C': 
            if (sign == '+') {
                gradeRange = "greater than or equal to 77%, but less than 80%.";
            }
            else if (sign == 'x' || sign == '-') {
                gradeRange = "greater than or equal to 70%, but less than 77%.";
            }
            break;

        case 'D': 
            if (sign == '+' || sign == '-' || sign == 'x') {
                gradeRange = "greater than or equal to 60%, but less than 70%.";
            }
            break;

        case 'F': 
            if (sign == '+' || sign == 'x' || sign == '-') {
                gradeRange = "less than 60%.";
            }
            break;

        default: 
            cout << "Oops, an error occured, please try again.";


    }// this is for closing switch 
    cout << "The student's letter grade range is " << gradeRange << endl;
    //u kept the cout statement in switch's block so it wouldn't work
    return 0;
} //this is for closing main

【讨论】：