String concatenation in MATLAB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is string concatenation in MATLAB?

String concatenation is the process of joining two or more strings end-to-end to form a new string.

beginner

How do you concatenate strings using square brackets in MATLAB?

str1 = 'Hello';
str2 = 'World';
result = ?

Use square brackets to join strings:

result = [str1 ' ' str2]; % result is 'Hello World'

intermediate

What function can you use to concatenate strings in MATLAB besides square brackets?

You can use the strcat function to concatenate strings without adding extra spaces.

intermediate

What is the difference between strcat and using square brackets for concatenation?

strcat removes trailing whitespace from input strings before concatenation, while square brackets keep all characters as is.

beginner

How do you concatenate strings with numbers in MATLAB?

Convert numbers to strings first using num2str, then concatenate. Example:

num = 5;
str = ['Value: ' num2str(num)]; % 'Value: 5'

Which of the following concatenates two strings with a space in MATLAB?

A 'Hello' + ' ' + 'World'

B ['Hello' ' ' 'World']

C strcat('Hello', ' ', 'World')

D concat('Hello', 'World')

Using square brackets with a space character joins the strings with a space. strcat removes trailing spaces but does not add spaces automatically.

What does strcat('Hi ', 'there') return?

A 'Hithere'

B 'Hi there'

C 'Hi there'

D Error

strcat removes trailing spaces before concatenation, so 'Hi ' becomes 'Hi', resulting in 'Hithere'.

How do you join the number 10 and string ' apples' into one string?

A ['10' ' apples']

B ['10' + ' apples']

C [num2str(10) ' apples']

D strcat(10, ' apples')

Numbers must be converted to strings with num2str before concatenation.

Which method keeps all spaces exactly as typed when concatenating?

A square brackets []

B strcat

C sprintf

D num2str

Square brackets concatenate strings exactly as they are, including spaces.

What is the output of ['A' 'B' 'C'] in MATLAB?

A Error

B 'A B C'

C ['A', 'B', 'C']

D 'ABC'

Square brackets join characters into one continuous string without spaces.

Explain how to concatenate two strings with a space between them in MATLAB.

Think about how to join strings exactly as you want them to appear.

Describe the difference between using strcat and square brackets for string concatenation.

Consider how spaces are treated in each method.

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