String concatenation in MATLAB - Step-by-Step Execution

Concept Flow - String concatenation

Start with strings

↓

Use concatenation operator

↓

Combine strings into one

↓

Store or display result

↓

End

This flow shows how MATLAB takes separate strings and joins them into one string using concatenation.

Execution Sample

MATLAB

str1 = 'Hello, ';
str2 = 'world!';
result = [str1 str2];
disp(result);

This code joins two strings "Hello, " and "world!" into one and prints it.

Execution Table

Step	Action	Variable	Value	Output
1	Assign string	str1	'Hello, '
2	Assign string	str2	'world!'
3	Concatenate	result	'Hello, world!'
4	Display	result	'Hello, world!'	Hello, world!

💡 All steps complete, concatenation done and output displayed.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
str1	undefined	'Hello, '	'Hello, '	'Hello, '	'Hello, '
str2	undefined	undefined	'world!'	'world!'	'world!'
result	undefined	undefined	undefined	'Hello, world!'	'Hello, world!'

Key Moments - 2 Insights

Why do we use square brackets [ ] for concatenation in MATLAB?

In MATLAB, square brackets combine arrays or strings horizontally. Here, [str1 str2] joins the two strings into one, as shown in step 3 of the execution_table.

What happens if we forget to use brackets and just write str1 str2?

MATLAB will give an error because it expects an operator or comma between variables. The brackets tell MATLAB to join the strings, as seen in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'result' after step 3?

A 'world!'

B 'Hello, world!'

C 'Hello,'

D undefined

💡 Hint

Check the 'Value' column for 'result' at step 3 in the execution_table.

At which step is the output 'Hello, world!' displayed?

A Step 2

B Step 3

C Step 4

D Step 1

💡 Hint

Look at the 'Output' column in the execution_table to find when the string is shown.

If we change str2 to 'MATLAB!', what will 'result' be after step 3?

A 'Hello, MATLAB!'

B 'Hello, world!'

C 'MATLAB! Hello, '

D 'Hello, '

💡 Hint

Refer to variable_tracker and understand concatenation order from the code.

Concept Snapshot

String concatenation in MATLAB:
- Use square brackets [ ] to join strings.
- Example: result = [str1 str2];
- Result is a new combined string.
- Use disp(result) to show the string.
- Forgetting brackets causes errors.

Full Transcript

This example shows how MATLAB joins two strings using square brackets. First, str1 is set to "Hello, ", then str2 to "world!". Using [str1 str2], MATLAB concatenates them into "Hello, world!" stored in result. Finally, disp(result) prints the combined string. The key is using brackets to join strings, as MATLAB treats them like arrays. Without brackets, MATLAB cannot combine strings and will error. This step-by-step trace helps beginners see how variables change and when output appears.

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