c# - 如何查看用户是否未在 C# 中输入有效条目

Question

我想知道如果用户在下面的代码中输入了无效条目，如何输出。例如，如果他们输入字符串字符或字符串字符和数字的组合。现在，如果输入无效条目，它只会中断程序。请保留最基本方法的答案，因为我对编程还很陌生!

 Console.Write("Please enter the persons age: ");
 int age = int.Parse(Console.ReadLine());
 if(age == 17)
 {
     Console.WriteLine("That's to bad! You will have to wait until next year!");
 }    
 else if (age < 18)
 {
     Console.WriteLine("That's to bad! You will have to wait a couple years until you can come in!");
 }
 else
 {
     Console.WriteLine("You are of age to be here.");
 }

 while (true)
 {
     Console.Write("Please enter the next persons age: ");
     age = int.Parse(Console.ReadLine());

     if (age == 17)
     {
         Console.WriteLine("That's to bad! You will have to wait until next year!");
     }
     else if (age < 18)
     {
         Console.WriteLine("That's to bad! You will have to wait a couple years until you can come in!");
     }
     else if (age > 18)
     {
          Console.WriteLine("You are of age to be here.");
     }
     else
     {
          Console.WriteLine("Please enter a valid entry");
     }
 }

Answer 1

你可以这样做:

int age;

if (int.TryParse(Console.ReadLine(), out age))
{
    if (age > 17)
    {
        Console.WriteLine("That's too bad! You will have to wait until next year!");
    }
    // etc
}
else
{
    Console.WriteLine("Please enter a valid input");
}

解释:

int.TryParse 是一种接受string 并尝试将其转换为int 的方法，如果转换成功则分配结果赋给age变量并返回true导致程序进入if block ，否则返回false并且程序进入否则 block 。 age 变量是通过使用 C# 的 output parameters feature 赋值的。这是一种将变量从外部传递给方法的方法，而后者 promise 会为其分配一些值。