在方法中返回新字符串

Question

I'm newbie to c#, So i tried the below program, which will change the case of the first character of the string

public class StringBuilder
    {
        public static string ChangeFirstLetterCase(string inputdata)
        {
            if(inputdata.Length > 0)
            {
                char[] charArray = inputdata.ToCharArray();
                charArray[0] = char.IsUpper(charArray[0]) ? 
                    char.ToLower(charArray[0]) : char.ToUpper(charArray[0]);
                //return new string(charArray);
                return charArray.ToString();
            }
            return inputdata;
        }
    }
class Program
    {
        static void Main(string[] args)
        {
            var a = StringBuilder.ChangeFirstLetterCase("vishnu");
            Console.WriteLine(a);
            Console.ReadLine();
        }
    }

Since the return type of this method ChangeFirstLetterCase() is a string. So I'm just doing the conversion like below

`return charArray.ToString();`

So in the method call it is returning the System.Char[]

Alternatively I tried the below one as well

`return new string(charArray);`

So this is returning the value as expected

Argument to the method - "vishnu"
Return value - "Vishnu"

So my question here is

1. Since the return type of the method is string, what's wrong with below conversion?

   return charArray.ToString();

2. How do we know when to return as new string?.

   return new string(charArray);

Please provide me some example

Answer 1

If you return the char array as a String, it will return you the name of the object System.Char[] . This is because the ToString method of char arrays does not build the characters of the array into a usable string, but simply makes a String that states the type of object.

However, if you use new String(char[]) , this will read the contents of the char array to build a string out of whatever characters are in the char array. So, you will want to use new String(char[]) for most of your String building, I cannot think of any real uses for using the ToString() on a char array.

So, for your example, you should use return new String(charArray); instead of return charArray.ToString(); .

Answer 2

charArray.ToString(); returns the type name because it's implemented that way, for getting string back from a character array you will always have to use String class constructor.

ToString method for char[] is not implemented in a way to return the character array back as a string literal, so use String constructor as you did in the second case.

Answer 3

You could return:

if(inputData[0].IsLower())
   return string.Concat(inputData[0].ToUpper(), inputData.Substring(1));  
else 
   return string.Concat(inputData[0].ToLower(), inputData.Substring(1)); 

Your value would already be a usable string and wouldn't need to have a char[].

I'm not really sure what you gain from converting the string to a char array to being with.