String concatenation in MATLAB

Introduction

String concatenation lets you join two or more pieces of text into one longer text. This helps when you want to build messages or combine words.

Creating a full sentence from separate words or phrases.

Building file paths by joining folder names and file names.

Combining user input with fixed text to show messages.

Making labels or titles by joining different text parts.

Syntax

MATLAB

newString = [string1 string2 ... stringN];

Use square brackets [ ] to join strings in MATLAB.

Strings can be character arrays (using single quotes) or string objects (using double quotes).

Examples

Joins two character arrays into one: 'Hello, world!'

MATLAB

greeting = ['Hello, ' 'world!'];

Joins string objects to make a welcome message.

MATLAB

name = "Alice";
welcome = ["Welcome, " name "!"];

Concatenates two character arrays with a space included.

MATLAB

part1 = 'Good';
part2 = ' Morning';
full = [part1 part2];

Sample Program

This program joins 'Hello, ', the name 'Bob', and '!' into one string and shows it.

MATLAB

name = "Bob";
greeting = ["Hello, " name "!"];
disp(greeting);

Important Notes

When using character arrays (single quotes), make sure to include spaces if needed.

String objects (double quotes) are easier to work with for text operations in newer MATLAB versions.

Use disp() to display the concatenated string on the screen.

Summary

Use square brackets [ ] to join strings in MATLAB.

You can join character arrays or string objects.

Concatenation helps build messages or combine text parts.

Practice

1. Which of the following is the correct way to concatenate two strings 'Hello' and 'World' in MATLAB?

easy

A. ['Hello' 'World']

B. 'Hello' + 'World'

C. concat('Hello', 'World')

D. 'Hello' & 'World'

Solution

1. Step 1: Understand MATLAB string concatenation syntax

   In MATLAB, square brackets [ ] are used to join strings or character arrays.

2. Step 2: Apply concatenation to given strings

   Using ['Hello' 'World'] joins the two strings into 'HelloWorld'. Other options use incorrect syntax.

3. Final Answer:

   ['Hello' 'World'] -> Option A

4. Quick Check:

   Use [ ] to join strings in MATLAB [OK]

Hint: Use square brackets [ ] to join strings in MATLAB [OK]

Common Mistakes:

• Using + operator for strings
• Using functions not defined in MATLAB
• Using & operator which is invalid for strings

2. Which of the following MATLAB statements correctly concatenates the strings 'Data' and '123'?

easy

A. str = 'Data' + '123';

B. str = strcat('Data', 123);

C. str = ['Data' '123'];

D. str = 'Data' & '123';

Solution

1. Step 1: Check syntax for string concatenation

   In MATLAB, concatenation uses square brackets [ ] for character arrays or strings.

2. Step 2: Evaluate each option

   str = ['Data' '123']; uses ['Data' '123'] which correctly joins the two strings. str = 'Data' + '123'; uses + which is invalid. str = strcat('Data', 123); uses strcat but passes a number without converting it to string. str = 'Data' & '123'; uses & which is invalid.

3. Final Answer:

   str = ['Data' '123']; -> Option C

4. Quick Check:

   Concatenate strings with [ ] brackets [OK]

Hint: Use [ ] brackets to join strings, not + or & [OK]

Common Mistakes:

• Using + operator for strings
• Passing numbers directly to strcat without conversion
• Using & operator for concatenation

3. What is the output of the following MATLAB code?

str1 = 'Good';
str2 = 'Morning';
result = [str1 ' ' str2];
disp(result);

medium

A. Good Morning

B. GoodMorning

C. Good_Morning

D. Error

Solution

1. Step 1: Analyze the concatenation expression

   The code concatenates str1, a space character ' ', and str2 using square brackets.

2. Step 2: Understand the output of disp

   The result is 'Good Morning' with a space between the words, so disp prints it exactly as 'Good Morning'.

3. Final Answer:

   Good Morning -> Option A

4. Quick Check:

   Concatenate with space inside [ ] to separate words [OK]

Hint: Add ' ' inside [ ] to insert space between strings [OK]

Common Mistakes:

• Forgetting to add space character
• Using + operator instead of [ ]
• Expecting underscore instead of space

4. The following MATLAB code is intended to concatenate 'Hi' and 'There' but causes an error. What is the error and how to fix it?

str1 = 'Hi';
str2 = 'There';
result = str1 + str2;
disp(result);

medium

A. No error, output is 'HiThere'

B. Error: Use strcat function instead of +

C. Error: Use & operator instead of +

D. Error: Use square brackets [ ] instead of + for concatenation

Solution

1. Step 1: Identify the cause of error

   Using + operator between strings in MATLAB causes an error because + is not defined for character arrays.

2. Step 2: Correct the concatenation method

   Replace + with square brackets [ ] to join strings: result = [str1 str2];

3. Final Answer:

   Error: Use square brackets [ ] instead of + for concatenation -> Option D

4. Quick Check:

   Concatenate strings with [ ], not + [OK]

Hint: Replace + with [ ] to fix string concatenation error [OK]

Common Mistakes:

• Using + operator for strings
• Trying to use & operator
• Assuming strcat always fixes + errors

5. You want to create a message in MATLAB that says 'User: John, Age: 30' by concatenating variables name = 'John' and age = 30. Which code correctly creates this message?

hard

A. msg = ['User: ' + name + ', Age: ' + string(age)];

B. msg = ['User: ' name ', Age: ' num2str(age)];

C. msg = strcat('User: ', name, ', Age: ', age);

D. msg = ['User: ' name ', Age: ' age];

Solution

1. Step 1: Understand variable types and concatenation

   name is a string, age is a number. To concatenate, age must be converted to string using num2str.

2. Step 2: Check each option for correctness

   msg = ['User: ' name ', Age: ' num2str(age)]; uses [ ] and num2str(age) correctly. msg = ['User: ' name ', Age: ' age]; tries to concatenate number directly causing error. msg = strcat('User: ', name, ', Age: ', age); uses strcat but passes number without conversion. msg = ['User: ' + name + ', Age: ' + string(age)]; uses + operator which is invalid.

3. Final Answer:

   msg = ['User: ' name ', Age: ' num2str(age)]; -> Option B

4. Quick Check:

   Convert numbers to strings before concatenation [OK]

Hint: Convert numbers to strings with num2str before concatenation [OK]

Common Mistakes:

• Concatenating numbers without conversion
• Using + operator for strings
• Passing numbers directly to strcat