一、预算符和表达式

1、条件 ref

ref 表示址引用

int[] smallArray = {1, 2, 3, 4, 5};
int[] largeArray = {10, 20, 30 ,40, 50};
int index = 7;
ref int refValue = ref((index < 5) ? ref smallArray[index] : ref largeArray[indeex - 5]);
refValue = 0;
index = 2;
ref((index < 5) ? ref smallArray[index] : largeArray[indeex - 5]) = 100;
Console.WriteLine(string.Join(" ", smallArray));
Console.WriteLine(string.Join(" ", largeArray));
//输出结果如下:
// 1 2 100 4 5
// 10 20 0 40 50

两个数交换(正常int传参是值传参,函数里交换,调用者不会变) 这时可以用ref

static void Main(string[] args) {
   int x = 20;
   int y = 30;
   Controle.WriteeLine($"交换前: x={x}; y={y}");
   TextRef( ref x, ref y);
   Controle.WriteeLine($"交换后: x={x}; y={y}");
}
static void TestRef(ref int x, ref int y) {
   int temp;
   temp = y;
   y = x;
   x = temp;
}

二、好用的语法

1、 String

1.1 string.join

int[] numbers = {2, 3, 4};
Console.WriteLine(string.join(" ", numbers));
//输出结果:
//2 3 4

2、Number

2.1 number.Select

int[] numbers = {2, 3, 4};
numbers.Select(x => x * x);
Console.WriteLine(string.join(" ", numbers));
//输出结果:
//4 9 16