c# - c# 中的减法？

Question

我不能在 C# 中从我的字典中减去项目

这是代码，我正在尝试获取水果。将其计数为 int。

public class test
{
    public static void Main()
    {
        int totalStock = 10;`

        Dictionary<string, int> fruits = new Dictionary<string, int>();
        fruits.Add("Apples", 3);
        fruits.Add("pears", 4);
        int fruitsCount = fruits["Apples" + "pears"];
        if(fruitsCount > totalStock){
            Console.WriteLine("You have too many fruits! Please get rid of " + fruitsCount - totalStock + " fruits");
        }
        else if(fruitsCount = totalStock){
            Console.WriteLine("You have just the right amount of fruits!");
        }
        else{
            Console.WriteLine("You can fit " + totalStock - fruitsCount + " fruits");
        }

    }
}

但是我收到错误:

exit status 1 main.cs(14,21): error CS0019: Operator `-' cannot beapplied to operands of type 'string' and 'int'

main.cs(16,10): errorCS0029: Cannot implicitly convert type 'int' to 'bool'

main.cs(20,21):error CS0019: Operator '-' cannot be applied to operands of type'string' and 'int'

Answer 1

你没有 "Apples"+ "pears"== "Applespears" 水果，这就是原因

fruits["Apples" + "pears"];

错了。把它写成 fruits["Apples"] + fruits["pears"];:

public static void Main() {
  int totalStock = 10;

  Dictionary<string, int> fruits = new Dictionary<string, int>() {
    {"Apples", 3},       
    {"pears", 4},
  };

  // Either Apples + pears
  int fruitsCount = fruits["Apples"] + fruits["pears"];
  // ... Or sum of all the fruits
  // int fruitsCount = fruits.Values.Sum();

  if (fruitsCount > totalStock){
    Console.WriteLine($"You have too many fruits! Please get rid of {fruitsCount - totalStock} fruits");
  }
  else if(fruitsCount == totalStock) { // should be comparison "==" not assignement "="
    Console.WriteLine("You have just the right amount of fruits!");
  }
  else {
    Console.WriteLine($"You can fit {totalStock - fruitsCount} fruits");
  }

注意string:我们不能减去string，只能减去整数；在你的情况下string interpolation是解决方案(我们在字符串中减去 整数):

  $"You have too many fruits! Please get rid of {fruitsCount - totalStock} fruits"

  $"You can fit {totalStock - fruitsCount} fruits"