C#控制台应用程序做while循环答案

【问题标题】：C# Console Application do while loopC#控制台应用程序做while循环
【发布时间】：2014-03-23 10:15:53
【问题描述】：

我对 do while 循环有疑问。当我这样做时。

它说：“再次”使用未分配的变量。我完全不知道为什么。

也许这是个愚蠢的问题..对不起，我刚开始学习如何编码，我对编程逻辑毫无感觉>

    static void Main(string[] args) {

        double WeightKg = 0.0, HeightCm = 0.0, Weightlbs = 0.0, WeightOz = 0.0, BMI = 0.0, Feet = 0.0, Inches = 0.0;
        int BMIOption;
        string again;

     do{
        string BMIMenu = ("Which Measurement You Want to use to enter the weight and height?"
                        + "\n1)Enter 1 for Metric"
                        + "\n2)Enter 2 for British Imperial:");
        Console.Write(BMIMenu);
        BMIOption = int.Parse(Console.ReadLine());

        if (BMIOption == 1) {
            Console.Write("\nPlease Enter your Weight in Kilogram (kg):");
            WeightKg = double.Parse(Console.ReadLine());
            Console.Write("\nPlease Enter your Height in in centimetres (cm):");
            HeightCm = double.Parse(Console.ReadLine());
            BMI = WeightKg / (HeightCm / 100 * HeightCm / 100);

            if (BMI >= 35.0) {
                Console.WriteLine("\nYour BMI is {0:G},Severe Obesity", BMI);
            } else if (BMI >= 30.0) {
                Console.WriteLine("\nYour BMI is {0:G},Obese", BMI);
            } else if (BMI >= 25.0) {
                Console.WriteLine("\nYour BMI is {0:G},OverWeight", BMI);
            } else if (BMI >= 18.5) {
                Console.WriteLine("\nYour BMI is {0:G},Healthy BodyWeight", BMI);
            } else if (BMI <= 18.5) {
                Console.WriteLine("\nYour BMI is {0:G},UnderWeight", BMI);
            }//End if
            Console.Write("\nWould you like to make an another conversion? \n\n(Enter Y to make an another conversion/Enter any other key to exit):");
            again = Console.ReadLine();

            } else if (BMIOption == 2) {
            Console.WriteLine("Please Enter your Weight in Pounds (lbs):");
            Weightlbs = double.Parse(Console.ReadLine());
            Console.WriteLine("Please Enter your Weight in Ounces (oz):");
            WeightOz = double.Parse(Console.ReadLine());
            Console.WriteLine("Please Enter your Height in Feet (ft):");
            Feet = double.Parse(Console.ReadLine());
            Console.WriteLine("Please Enter your Height in Inches (ins):");
            Inches = double.Parse(Console.ReadLine());

            WeightKg = ((Weightlbs * 16) + WeightOz) / 35.2;
            HeightCm = ((Feet * 12) + Inches) * 2.54;
            BMI = WeightKg / (HeightCm / 100 * HeightCm / 100);

            if (BMI >= 35) {
                Console.WriteLine("Your BMI is {0:G},Severe Obesity", BMI);
            } else if (BMI >= 30) {
                Console.WriteLine("Your BMI is {0:G},Obese", BMI);
            } else if (BMI >= 25) {
                Console.WriteLine("Your BMI is {0:G},OverWeight", BMI);
            } else if (BMI >= 18.5) {
                Console.WriteLine("Your BMI is {0:G},Healthy BodyWeight", BMI);
            } else if (BMI <= 18.5) {
                Console.WriteLine("Your BMI is {0:G},UnderWeight", BMI);
            }//End if
            Console.Write("\nWould you like to make an another conversion? \n\n(Enter Y to make an another conversion/Enter any other key to exit):");
            again = Console.ReadLine();
           }
     } while (again == "y" || again == "Y");
    }
}

}

【问题讨论】：

标签： c# console-application calculator

【解决方案1】：

如果您只关注代码的重要部分，您会得到：

string again;
do {
  ...
  if (BMIOption == 1) {
    ...
    again = Console.ReadLine();
  } else if (BMIOption == 2) {
    ...
    again = Console.ReadLine();
  }
} while (again == "y" || again == "Y");

如您所见，如果 BMIOption 与 1 或 2 不同，那么 again 将不会被初始化。您很可能应该将要在 ifs 之外分配 another 的语句移动，如下所示：

do {
  ...
  if (BMIOption == 1) {
    ...
  } else if (BMIOption == 2) {
    ...
  }
  again = Console.ReadLine();
} while (again == "y" || again == "Y");

您也可以使用其他人建议的值初始化 again 变量，但如果 BMIOption 不同于 1 或 2，则不会更新 again。

【讨论】：

【解决方案2】：

您的string again 未分配，并且您不能假设在do-while 循环中检查它时它总是有一个值。只需将其初始化为任何值，例如string again="";

【讨论】：

【解决方案3】：

编译器错误是因为您声明了一个名为 again 的变量，但您没有（总是）在使用它之前为其赋值。

如果您不输入分配它的if-blocks 之一，您需要决定again 应该具有什么值。

您可能希望在声明时将其初始化为null：

string again = null;

【讨论】：

【解决方案4】：

if (BMIOption == 1) {

将再次设置。但是如果 is != 并且 is != 2 则永远不会再设置。添加到 if 语句 un else 你再次设置或声明变量并赋值

string again = string.Empty;

【讨论】：