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1，一个参数只有在引用的时候才能改变其值，这是一种情况
2，一个参数在引用后要永久的改变其值（可以用返回参数的形式）
3，多个参数在引用后要永久的改变其值或者多个参数中的部分（返回参数就适合了，因为只能返回一个，所以就用REF和4.OUT了）
上例子
1
static void ShowDouble(int val) { val *= 2; Console.WriteLine("val doubled = {0}", val); } int myNumber = 5; Console.WriteLine("myNumber = {0}", myNumber); ShowDouble(myNumber); Console.WriteLine("myNumber = {0}", myNumber);
2
static int DoubleNum(int val) { val *= 2; return val; } int myNumber = 5; Console.WriteLine("myNumber = {0}", myNumber); myNumber = DoubleNum(myNumber); Console.WriteLine("myNumber = {0}", myNumber);
3。REF
static void ShowDouble(ref int val) { val *= 2; Console.WriteLine("val doubled = {0}", val); } int myNumber = 5; Console.WriteLine("myNumber = {0}", myNumber); ShowDouble(ref myNumber); Console.WriteLine("myNumber = {0}", myNumber);
4. OUT
static int MaxValue(int[] intArray, out int maxIndex) { int maxVal = intArray[0]; maxIndex = 0; for (int i = 1; i < intArray.Length; i++) { if (intArray[i] > maxVal) { maxVal = intArray[i]; maxIndex = i; } } return maxVal; } int[] myArray = { 1, 8, 3, 6, 2, 5, 9, 3, 0, 2 }; int maxIndex; Console.WriteLine("The maximum value in myArray is {0}", MaxValue(myArray, out maxIndex)); Console.WriteLine("The first occurrence of this value is at element {0}", maxIndex + 1);
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原文地址：http://www.cnblogs.com/mamiyiya777/p/5939472.html
