C# String Join() Method

The Join() method in C# is used to concatenate an array of strings into a single string, with a specified separator between each element of the array. It returns a new string that contains the concatenated elements of the array, separated by the specified separator.

The syntax of the Join() method is as follows:

string.Join(separator, values);

Here, separator is the string to use as a separator between the elements of the array, and values is the array of strings to concatenate.

For example, to concatenate an array of strings with a comma separator, you can use the following code:

string[] fruits = { "apple", "banana", "cherry" };
string result = string.Join(",", fruits);
Console.WriteLine(result);  // Output: "apple,banana,cherry"

In this example, the Join() method is used to concatenate the array of strings { "apple", "banana", "cherry" } with a comma separator. The resulting string "apple,banana,cherry" is then assigned to the result variable and printed to the console using the WriteLine() method.

You can use any string as a separator, including an empty string. For example, to concatenate an array of strings with no separator, you can use the following code:

string[] fruits = { "apple", "banana", "cherry" };
string result = string.Join("", fruits);
Console.WriteLine(result);  // Output: "applebananacherry"

In this example, the Join() method is used to concatenate the array of strings { "apple", "banana", "cherry" } with an empty separator. The resulting string "applebananacherry" is then assigned to the result variable and printed to the console.

You can also use the Join() method to concatenate a subset of the elements of an array, starting from a specified index and including a specified number of elements. To do this, you can use the following syntax:

string.Join(separator, values, startIndex, count);

Here, startIndex is the zero-based index of the first element to concatenate, and count is the number of elements to concatenate. For example:

string[] fruits = { "apple", "banana", "cherry", "date", "elderberry" };
string result = string.Join(",", fruits, 2, 3);
Console.WriteLine(result);  // Output: "cherry,date,elderberry"

In this example, the Join() method is used to concatenate the three elements starting from the index 2 of the array { "apple", "banana", "cherry", "date", "elderberry" } with a comma separator. The resulting string "cherry,date,elderberry" is then assigned to the result variable and printed to the console.