Dart String Concatenation

Append or Concatenate Two Strings in Dart

String concatenation combines two or more strings into one string. In Dart, you can concatenate strings with the + operator, place adjacent string literals next to each other, or use string interpolation when values need to be inserted into text.

The most direct way to append one string to another is:

String result = firstString + secondString;

The + operator accepts strings as operands and returns a new string containing their combined characters. Dart strings are immutable, so the original strings are not modified.

Concatenate Two Dart Strings with the + Operator

In this example, we will take two Dart Strings and concatenate them using +.

Dart Program

void main(){
	
	String str1 = 'Tutorial';
	String str2 = 'Kart';
	
	//concatenate str1 and str2
	String result = str1 + str2;
	
	print(result);
}

Output

TutorialKart

No separator is inserted automatically. Because str1 does not end with a space and str2 does not begin with one, the result is TutorialKart.

Add Spaces Between Concatenated Strings in Dart

Include a space explicitly when the combined strings represent separate words. The space can be added to either string or supplied as another string operand.

void main() {
  String firstName = 'Alex';
  String lastName = 'Morgan';

  String fullName = firstName + ' ' + lastName;

  print(fullName);
}

Output

Alex Morgan

Concatenate More Than Two Strings in Dart

In this example, we will take three Dart Strings and concatenate them using +. We can chain the + operator. Hence, we can concatenate more than two strings in a single statement. Please observe the below example.

Dart Program

void main(){
	
	String str1 = 'Welcome to ';
	String str2 = 'Tutorial';
	String str3 = 'Kart';
	
	//concatenate str1, str2 and str3
	String result = str1 + str2 + str3;
	
	print(result);
}

Output

Welcome to TutorialKart

Dart evaluates this expression from left to right. Each + operation creates a combined string that is used by the next operation.

Join Adjacent String Literals Without the + Operator

Dart automatically combines adjacent string literals. This is useful when a long fixed message is split across multiple lines in the source code.

void main() {
  String message = 'Dart supports '
      'adjacent string literals.';

  print(message);
}

Output

Dart supports adjacent string literals.

This form works only with string literals written directly in the code. Variables still require the + operator, interpolation, or another string-building method.

Concatenate Dart Strings with String Interpolation

String interpolation is usually easier to read when a message contains variables. Use $variableName for a simple variable or ${expression} for an expression.

void main() {
  String language = 'Dart';
  String topic = 'string concatenation';

  String message = 'Learn $topic in $language.';

  print(message);
}

Output

Learn string concatenation in Dart.

Braces are needed when accessing a property, performing a calculation, or separating a variable name from following text.

void main() {
  String item = 'book';
  int quantity = 3;

  String message = 'Order: $quantity ${item}s';

  print(message);
}

Output

Order: 3 books

Concatenate a Dart String with an int

You can concatenate String with other type of objects. All you need to do is convert the other type of Dart object to String using object.toString() method.

In this example, we will take a String and an int and concatenate them using +. During concatenation, we convert the int to string.

Dart Program

void main(){
	
	String str1 = 'Welcome to ';
	int n = 24;
	
	//concatenate str1 and n
	String result = str1 + n.toString();
	
	print(result);
}

Output

Welcome to 24

String interpolation provides a shorter alternative because Dart converts the interpolated value to its string representation automatically.

void main() {
  int lessons = 24;
  String result = 'Welcome to lesson $lessons';

  print(result);
}

Output

Welcome to lesson 24

Build a Dart String Repeatedly with StringBuffer

For a small number of values, the + operator and interpolation are straightforward. When a string is assembled repeatedly inside a loop, StringBuffer provides a dedicated way to collect text and create the final string once.

void main() {
  var buffer = StringBuffer();

  for (int i = 1; i <= 3; i++) {
    buffer.write('Item $i');

    if (i < 3) {
      buffer.write(', ');
    }
  }

  String result = buffer.toString();
  print(result);
}

Output

Item 1, Item 2, Item 3

The write() method appends text without inserting a line break. Use writeln() when each appended value should end with a newline.

Join a List of Dart Strings with a Separator

When the values are already stored in a list, use the list’s join() method. The argument passed to join() is inserted between consecutive elements.

void main() {
  List<String> words = ['Learn', 'Dart', 'Programming'];

  String sentence = words.join(' ');

  print(sentence);
}

Output

Learn Dart Programming

Choose the Appropriate Dart String Concatenation Method

Requirement	Recommended approach
Combine two or three string variables	Use the + operator
Insert variables or expressions into readable text	Use string interpolation
Split a fixed string literal across source lines	Use adjacent string literals
Combine list elements with a delimiter	Use join()
Append text repeatedly, especially in a loop	Use StringBuffer

Common Dart String Concatenation Mistakes

• Missing spaces: Dart does not add spaces between concatenated strings. Add ' ' where needed.
• Combining a String and int directly: Convert the number with toString() when using +, or use interpolation.
• Forgetting interpolation braces: Use ${...} for expressions, property access, and cases where the variable name must be clearly separated from adjacent text.
• Expecting the original string to change: Concatenation returns a new string because Dart strings are immutable. Assign the result to a variable.
• Using repeated + operations in a large loop: Use StringBuffer when text is appended many times.

Frequently Asked Questions About Dart String Concatenation

How do I concatenate two strings in Dart?

Place the + operator between the strings, as in String result = first + second;. Add a separate space string when the values should be displayed as separate words.

Can I concatenate a String and an int in Dart?

Yes. Convert the integer with toString() before using +, or insert it with string interpolation, such as 'Count: $count'.

What is the difference between + and string interpolation in Dart?

The + operator explicitly combines string operands. Interpolation inserts variables or expressions inside a string literal and is often easier to read when constructing sentences.

How do I concatenate strings with a newline in Dart?

Insert the newline escape sequence \n between the values, use a multiline string, or call writeln() on a StringBuffer.

When should I use StringBuffer instead of + in Dart?

Use StringBuffer when text is appended repeatedly, such as during a loop. For a small, fixed number of strings, + or interpolation is usually simpler.

Summary of Dart String Concatenation

In this Dart Tutorial, we learned how to append or concatenate two ore more strings.

Use + for direct concatenation, interpolation for readable strings containing values, join() for lists, and StringBuffer for repeated appends. Remember to add spaces, punctuation, and newline characters explicitly where the final text requires them.