C# String - Join() Method

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The C# String Join() method is used to concatenate the element of an array or collection into a single string, with a specified delimiter separating each element or member.

It can be overloaded based on the argument of the join method.

Syntax

Following is the syntax of the C# string Join() method −

string String.Join(string separator, IEnumerable<string> values);
string String.Join(string separator, string[] values);

Parameters

This method accepts the following parameters −

• separator: It represents a string that separates the concatenated elements (e.g., a comma ",", a space " ", etc.).
• values: It represents a collection (IEnumerable<string> or string[]) whose elements will be concatenated.

Return Value

This method returns a string that contains elements of values parameter delimited by the separator character.

Example 1: Joining an Array of String

Following is a basic example of the Join() method to join the array of strings into a single string −

  
using System;
class Program {
   static void Main() {
      string[] words = { "This", "is", "tutorialspoint" };
      string result = String.Join(", ", words);
      Console.WriteLine(result);
   }
}

Output

Following is the output −

This, is, tutorialspoint

Example 2: Joining With Custom Delimiter

Let's look at another example. Here, we use the Join() method to convert a character array into a single string −

using System;
class Program {
   static void Main() {
      char[] letter = { 'A', 'B', 'C' };
      string result = String.Join("|", letter);
      Console.WriteLine(result);
   }
}

Output

Following is the output −

A|B|C

Example 3: Use Join Method with StartIndex and Count

Here, in this example, we use the Join() method with startIndex and count. It will only concatenate the string from the starting index to the specified number of elements −

using System;
class Program {
   static void Main() {
      String[] val = {
         "This",
         "is",
         "green",
         "apple",
         "you",
         "want to",
         "buy"
      };
      String sep = ", ";
      String result;

      Console.WriteLine("val[] = {{'{0}' '{1}' '{2}' '{3}'}}", val[0], val[1], val[2], val[3]);
      result = String.Join(sep, val, 1, 4);
      Console.WriteLine("String.Join(sep, val, 1, 4) = '{0}'", result);
   }
}

Output

Following is the output −

val[] = {'This' 'is' 'green' 'apple'}
String.Join(sep, val, 1, 4) = 'is, green, apple, you'

Example 4: Joining with Null or Empty Values:

The example below uses the Join() method to join the string array into a single string. The join method treats null elements as empty strings (""). −

using System;
class Program {
   static void Main(){
      // array with null value
      string[] items = { "A", null, "C", "D" };
      string result = String.Join(", ", items);
      Console.WriteLine(result);
   }
}

Output

Following is the output −

A, , C, D