C# String Concat() Method
Definition
In C#, String.Concat() joins strings into one new string. It does not insert a separator between pieces.
You pass the pieces to join. At least one value is required in normal use. The inputs are not changed. The result is a new string.
Syntax
Pass the pieces to join. Start with this call.
string s = string.Concat("Code", "To", "Fun");
| Call | What it does |
|---|
string.Concat("Code", "To", "Fun") | Joins the pieces into CodeToFun with no spaces. |
This is a static method. For a separator between items, use string.Join.
Library declarations
public static string Concat(string str0, string str1);
public static string Concat(params string[] values);
Parameters
| Parameter | Description |
|---|
| str0 | Required. The first string. |
| str1 | Required. The second string. |
| values | Optional. More strings when you use the params overload. |
Return Value
| Return Value | Description |
|---|
| New string | The joined text. Empty pieces become empty text. |
C# Examples
Example 1 — Join First and Last Name
Build a full name with an explicit space separator between two strings.
using System;
class Program {
static void Main() {
string first = "John";
string last = "Doe";
string fullName = string.Concat(first, " ", last);
Console.WriteLine(fullName);
Console.WriteLine($"first still: {first}");
}
}
John Doe
first still: John
How It Works
- Call the static method.
string.Concat(first, " ", last) joins three pieces in order. - Include the separator. The space is its own argument—Concat does not insert separators automatically.
- Get a new string.
fullName is "John Doe". - Inputs stay unchanged.
first is still "John" because strings are immutable.
Example 2 — Concat an Array (or params)
Pass a string[] or several arguments—both join left to right with no separator between items.
using System;
class Program {
static void Main() {
string[] parts = { "Code", "To", "Fun" };
string glued = string.Concat(parts);
string spaced = string.Concat(parts[0], " ", parts[1], " ", parts[2]);
Console.WriteLine(glued);
Console.WriteLine(spaced);
}
}
How It Works
- Array overload.
Concat(parts) joins every element with nothing between → "CodeToFun". - Add spaces yourself. Pass separators as extra arguments when you need gaps.
- Need commas between items? Prefer string.Join(", ", parts)—built for delimiters.
- Params works the same.
Concat("A", "B", "C") is equivalent to joining those three strings.
Example 3 — Null Becomes Empty
null string arguments are skipped as empty text—safe, but easy to miss when debugging missing words.
using System;
class Program {
static void Main() {
string middle = null;
string result = string.Concat("Hello", middle, "!");
Console.WriteLine(result);
Console.WriteLine($"Length: {result.Length}");
}
}
How It Works
- Pass null in the middle.
middle is null. - Concat substitutes empty.
"Hello" + "" + "!" → "Hello!". - No exception. Unlike some APIs, Concat does not throw on null string args.
- Watch missing text. If a name is unexpectedly blank, check for null inputs—not a printed
"null".
Frequently Asked Questions
Concat() joins strings into one new string with no separator.
Pass the strings to join. Common overloads take two strings or a params array.
A new string with all pieces joined.
No. Strings are immutable. The inputs stay the same.
Use string.Join(separator, values) when you need commas or spaces between items.
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