C#-为什么在通过方法放置此变量后不更改 [英] C# - Why is this variable not being changed after being put through a method

问题描述

因此，我显然是编程新手，但正在尝试弄清为什么它不起作用

So I'm obviously fairly new to programming, but am trying to figure out why this isn't working

我正在尝试使用字符串myname，并将Mr.添加到它的开头.我知道我可以像myname = "Mr. " + myname一样简单地完成它，但是我试图了解如何使用方法来更改变量的值.那么，为什么不更改呢?

I'm trying to take the string myname, and add Mr. to the start of it. I know I could do it simply as just myname = "Mr. " + myname however I'm trying to understand how to use methods to change the values of variables. So, why doesn't this change?

public class Program
    {
        public static void Main(string[] args)
        {
            string myname = "harry";
            Console.WriteLine(myname); //output is harry

            namechanger(myname); //this should modify harry to Mr. Harry
            Console.WriteLine(myname); //output is still harry?
        }

        static string namechanger(string name) 
        {
            name = "Mr. " + name;
            return name;
        }

    }

推荐答案

字符串是不可变的和按值传递.每次创建字符串时，它都永远不会更改.因此，与类实例不同，您无法通过将字符串交给修改它的方法来修改它.

Strings are immutable, and passed by value. Every time you create a string, it will never be changed. So unlike instances of classes, you cannot modify a string by handing it to a method which modifies it.

在这种情况下，由于您在namechanger中return修改过的String，因此您要做的就是确保将myname分配给该方法的结果.像这样

In this case, since you return the modified String in namechanger, all you need to do is make sure you assign myname to the result of that method; like so

myname = namechanger(myname);

原始类型(int，float，long等)以这种方式工作，struct实例也是如此-因此，如果您不确定为什么要使用将struct的值传递给方法时，其值不会改变.

Primitive types (int, float, long, etc) work this way, as do struct instances - so be sure to look for that in the future, if you're ever unsure why a struct's value is not changing when you pass it into a method.

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