Question

我正在尝试创建一个程序，通过记录每个主题中获得的标记数来计算考试结果。它几乎完成但我遇到一个错误，即如果用户只是按Enter而不是输入值，应用程序将不会继续。还有什么方法可以缩短这段代码吗？

Console.WriteLine("Danyal's result calculator for students of class IX. Enter the marks requested, if not applicable leave blank and press enter :)");
Console.Write("Enter your Urdu marks: ");
int urdu = int.Parse(Console.ReadLine());
Console.Write("Enter your Maths marks: ");
int maths = int.Parse(Console.ReadLine());
Console.Write("Enter your English Literature marks: ");
int lit = int.Parse(Console.ReadLine());
Console.Write("Enter your Biology marks: ");
int bio = int.Parse(Console.ReadLine());
Console.Write("Enter your Chemistry marks: ");
int chem = int.Parse(Console.ReadLine());
Console.Write("Enter your Islamiat marks: ");
int isl = int.Parse(Console.ReadLine());
Console.Write("Enter your Physics marks: ");
int physics = int.Parse(Console.ReadLine());
Console.Write("Enter your Computer marks: ");
int comp = int.Parse(Console.ReadLine());
Console.Write("Enter your English Language marks: ");
int lang = int.Parse(Console.ReadLine());
Console.Write("Enter your Pakistan Studies marks: ");
int pst = int.Parse(Console.ReadLine());


int total = urdu + maths + lit + lang + bio + chem + physics + isl + comp + pst;
Console.WriteLine("Your total marks are {0} out of 1000", total);
float percentage = total * 100 / 1000;
Console.WriteLine("Your percentage is: {0}%",percentage);
Console.WriteLine("Note: the percentage has been rounded off. Please share this program with other classmates, also I am open to suggestions for creating more helpful programs.");
Console.ReadLine();

Answer 1

如果用户将其留空或输入无效值，我不确定您想要做什么，但您可以这样做。

        Dictionary<string,int> grades = new Dictionary<string, int>
        {
            { "Urdu", 0 },
            { "Maths", 0 },
            { "English", 0 },
            { "Biology", 0 },
            { "Chemistry", 0 },
            { "Islamiat", 0 },
            { "Physics", 0 },
            { "Computer", 0 },
            { "English Language", 0 },
            { "Pakistan Studies", 0 },
        };

        foreach (string grade in grades.Keys.ToArray())
        {
            Console.WriteLine(string.Format("Enter your {0} marks: ", grade));
            int mark;
            if (int.TryParse(Console.ReadLine(), out mark))
                grades[grade] = mark;
        }
        int total = grades.Sum((g) => g.Value);

在此示例中，如果使用错误输入，则成绩将默认为0.如果您愿意，可以将if try解析更改为循环并请求一个好的值，直到输入一个。

Answer 2

这是一个不遵守DRY原则的明显案例。您正在重复基本相同的操作，不要这样做。重构代码，以便在一个地方解决常见的模式或行为。

你会怎么做？

创建一个提示用户输入特定信息的方法。用户需要什么？描述他必须做什么的信息。用户需要做什么？输入有效输入。好的，考虑到这一点，以下方法的原型似乎是一个很好的起点：
```
private static int GetUserInput(string message) { ... }
```
嗯...输入有效输入。这意味着我们需要某种验证，所以再次让我们想一想如何解决这个问题：
```
private static int ValidateUserInput(string input) { ... }
```
这够好吗？嗯......不太好。如果用户输入的号码不正确会怎样？没有方便的方式来传达输入对呼叫者无效。我们可以返回-1，或者我们可以抛出一个异常，但两者看起来都很糟糕。

最好的解决方案是返回两个值;一个告诉我们输入是否有效，另一个告诉我们输入是什么。在c＃中，这并不是非常严格（至少在c＃7出现之前）。这样做的方法是使用out参数：
```
private static bool ValidateUserInput(string message, out int input) { ... }
```
现在这种方法完全符合我们的目的。返回值告诉我们输入是否有效，out参数input为我们提供了验证值（或者如果验证失败，我们就会忽略它。）
如果您基本上只想要总和和平均值，为什么要为每个标记创建一个int变量？让我们创建一个List<int>，我们存储所有标记。

另一个选项是，如果要跟踪哪个标记对应于哪个主题，将使用Dictionary<string, key>，其中键是主题名称，值是其对应标记。但是现在让我们使用List<int>。

考虑到这些，我们可以建立我们的解决方案：

public static void ComputeMarksSummary()
{
     var marks = new List<int>();

     marks.Add(GetUserInput("Enter your Urdu marks: "));
     marks.Add(GetUserInput("Enter your Maths marks: : "));
     marks.Add(GetUserInput("Enter your English Literature marks: "));
     marks.Add(GetUserInput("Enter your Biology marks: "));
     marks.Add(GetUserInput("Enter your Chemistry marks: "));
     marks.Add(GetUserInput("Enter your Islamiat marks: "));
     marks.Add(GetUserInput("Enter your Computer marks: "));
     marks.Add(GetUserInput("Enter your English language marks: "));
     marks.Add(GetUserInput("Enter your Pakistan studies marks: "));

     var total = marks.Sum();
     Console.WriteLine("Your total marks are {0} out of 1000", total);
     Console.WriteLine("Your percentage is: {0}%", total/10.0); //note the 10.0 to force double division, not integer division where 44/10 would be 4 not 4.4
     Console.WriteLine("Note: the percentage has been rounded off. Please share this program with other classmates, also I am open to suggestions for creating more helpful programs.");
     //WRONG! Percentage is not rounded off, its truncated: 9/10 is 0 in integer division.
     Console.ReadLine();
}

private static int GetUserInput(string message)
{
     int mark;

     while (true)
     {
          Console.WriteLine(message);
          var input = Console.ReadLine();

          if (!ValidateUserInput(input, out mark))
          {
               Console.WriteLine("Invalid input, please try again.");
          }
          else
          {
               return mark;
          }
     }
}

private static bool ValidateUserInput(string message, out int input)
{ 
    //left as an excerice. Hint: look into int.TryParse(...);
    //here you could decide if a blank input should be valid and parsed as zero. 
}

marks.Add(....)

public static void ComputeMarksSummary(IEnumerable<string> subjectNames)
{
     var marks = new List<int>();

     foreach (var subject in sujectNames)
     {
         marks.Add(GetUserInput(string.Format("Enter your {0} marks: ", subject)));
     }

     var total = marks.Sum();
     Console.WriteLine("Your total marks are {0} out of 1000", total);
     Console.WriteLine("Your percentage is: {0}%", total/10.0); //note the 10.0 to force double division, not integer division where 44/10 would be 4 not 4.4
     Console.WriteLine("Note: the percentage has been rounded off. Please share this program with other classmates, also I am open to suggestions for creating more helpful programs.");
     Console.ReadLine();
}

你可以这样称呼它：

ComputeMarksSummary(new string[] { "Urdu", "Maths", ... );

看起来那么干净吗？

我如何接受C＃中的空白？

2 个答案: