Converting between types in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to convert the number 5 to a string.

MATLAB

str_num = [1](5);

Drag options to blanks, or click blank then click option'

Anum2str

Bint2str

Cstring

Dchar

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'char' which converts numbers to characters but not strings.

Using 'string' which is for string arrays, not simple conversion here.

The num2str function converts numbers to strings in MATLAB.

2fill in blank

medium

Complete the code to convert the string '123' to a number.

MATLAB

num_val = [1]('123');

Drag options to blanks, or click blank then click option'

Astring

Bnum2str

Cstr2num

Dint2str

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'num2str' which converts numbers to strings, not the other way.

Using 'string' which converts to string arrays.

The str2num function converts strings to numbers in MATLAB.

3fill in blank

hard

Fix the error in converting the number 65 to a character.

MATLAB

char_val = [1](65);

Drag options to blanks, or click blank then click option'

Aint2str

Bnum2str

Cstring

Dchar

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'num2str' which converts numbers to strings, not characters.

Using 'string' which creates string arrays.

The char function converts numeric ASCII codes to characters in MATLAB.

4fill in blank

hard

Fill both blanks to convert the string '45' to a double and then back to a string.

MATLAB

num_val = [1]('45');
str_val = [2](num_val);

Drag options to blanks, or click blank then click option'

Astr2double

Bnum2str

Cstr2num

Dchar

Attempts:

3 left

💡 Hint

Common Mistakes

Using str2num instead of str2double which is more precise.

Using char which is for characters, not numbers.

str2double converts a string to a double number, and num2str converts a number back to a string.

5fill in blank

hard

Fill all three blanks to convert the number 50 to a character, then to a string, and finally back to a number.

MATLAB

char_val = [1](50);
str_val = [2](char_val);
num_val = [3](str_val);

Drag options to blanks, or click blank then click option'

Achar

Bstring

Cstr2double

Dnum2str

Attempts:

3 left

💡 Hint

Common Mistakes

Using num2str instead of string for character to string conversion.

Using str2num instead of str2double for string to number conversion.

First, char converts number to character. Then string converts character to string. Finally, str2double converts string back to number.

Practice

1. Which MATLAB function converts a string like '123.45' into a numeric double value?

easy

A. char

B. int32

C. str2double

D. num2str

Solution

1. Step 1: Understand the input and desired output

   The input is a string representing a number, and we want a numeric double value.

2. Step 2: Identify the correct conversion function

   str2double converts strings to double precision numbers, while int32 converts numbers to integers, char converts numbers to characters, and num2str converts numbers to strings.

3. Final Answer:

   str2double -> Option C

4. Quick Check:

   String to double = str2double [OK]

Hint: Use str2double for string to number conversion [OK]

Common Mistakes:

• Using int32 on strings causes errors
• Using char converts numbers to characters, not numbers
• Using num2str converts numbers to strings, not the other way

2. Which of the following is the correct syntax to convert the number 3.7 to an integer in MATLAB?

easy

A. int32(3.7)

B. int(3.7)

C. integer(3.7)

D. toInt(3.7)

Solution

1. Step 1: Recall MATLAB integer conversion functions

   MATLAB uses functions like int32, int16, etc., to convert numbers to integers.

2. Step 2: Check syntax correctness

   int32(3.7) is valid syntax; the others are not MATLAB functions.

3. Final Answer:

   int32(3.7) -> Option A

4. Quick Check:

   Correct integer conversion = int32(3.7) [OK]

Hint: Use int32() to convert decimals to integers [OK]

Common Mistakes:

• Using non-existent functions like int() or integer()
• Forgetting parentheses in function calls
• Expecting rounding instead of truncation

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

val = int32(5.9);
disp(val);

medium

A. 5

B. Error

C. 5.9

D. 6

Solution

1. Step 1: Understand int32 conversion behavior

   Converting a decimal number to int32 truncates the decimal part, it does not round.

2. Step 2: Apply truncation to 5.9

   Truncating 5.9 results in 5, so val becomes 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   int32 truncates decimals = 5 [OK]

Hint: int32 cuts decimals, does not round [OK]

Common Mistakes:

• Assuming int32 rounds up
• Expecting output to be 5.9 (no conversion)
• Thinking it causes an error

4. The following MATLAB code throws an error. What is the problem?

num = '123';
val = int32(num);

medium

A. Variable name 'num' is reserved

B. int32 cannot convert strings directly

C. Missing semicolon after assignment

D. int32 only works with integers, not strings

Solution

1. Step 1: Analyze the input type

   The variable num is a string, not a numeric value.

2. Step 2: Check int32 input requirements

   int32 expects numeric input, not strings. To convert a string to a number, use str2double first.

3. Final Answer:

   int32 cannot convert strings directly -> Option B

4. Quick Check:

   int32 needs numeric input [OK]

Hint: Convert string to number before int32 [OK]

Common Mistakes:

• Trying to convert string directly with int32
• Ignoring type mismatch errors
• Assuming int32 rounds strings

5. You have a cell array of strings representing numbers: {'10.5', '20.1', '30.9'}. Which MATLAB code correctly converts this to an integer array by truncating decimals?

hard

A. intArray = str2double(int32(cellArray));

B. intArray = int32(cellArray);

C. intArray = int32(str2num(cellArray));

D. intArray = int32(cellfun(@str2double, cellArray));

Solution

1. Step 1: Understand cell array conversion

   Each string in the cell array must be converted individually to a number.

2. Step 2: Use cellfun with str2double and then int32

   cellfun(@str2double, cellArray) converts each string to double, then int32 truncates decimals for the whole array.

3. Step 3: Check other options

   intArray = str2double(int32(cellArray)); tries to convert the cell array to int32 first, which fails. intArray = int32(cellArray); tries int32 on strings directly, which errors. intArray = int32(str2num(cellArray)); uses str2num incorrectly on cell array.

4. Final Answer:

   intArray = int32(cellfun(@str2double, cellArray)); -> Option D

5. Quick Check:

   Use cellfun + str2double + int32 [OK]

Hint: Use cellfun with str2double before int32 [OK]

Common Mistakes:

• Trying to convert whole cell array at once
• Using int32 directly on strings
• Confusing str2num with str2double on cell arrays