Type conversion functions in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of converting string to double and back

What is the output of this MATLAB code?

MATLAB

x = '123.45';
y = str2double(x);
z = num2str(y);
disp(z);

A 123.45

B '123.45'

C Error: Conversion failed

D 12345

💡 Hint

str2double converts string to number, num2str converts number back to string.

str2double converts the string '123.45' to the numeric value 123.45. num2str converts the number back to the string '123.45'. disp prints the string without quotes.

❓ Predict Output

intermediate

Result of logical to double conversion

What is the output of this MATLAB code?

MATLAB

a = true;
b = double(a);
disp(b);

A true

B 1

C 0

D Error: Cannot convert logical to double

💡 Hint

Logical true converts to 1 as a double.

In MATLAB, logical true converts to double 1. disp prints the numeric value 1.

❓ Predict Output

advanced

Output of converting numeric array to char

What is the output of this MATLAB code?

MATLAB

nums = [65 66 67];
chars = char(nums);
disp(chars);

A ABC

B [65 66 67]

C Error: Cannot convert numeric array to char

D abc

💡 Hint

char converts numeric ASCII codes to characters.

65, 66, 67 are ASCII codes for 'A', 'B', 'C'. char converts them to the string 'ABC'.

❓ Predict Output

advanced

Result of converting cell array of strings to numeric array

What is the output of this MATLAB code?

MATLAB

c = {'1', '2', '3'};
n = str2double(c);
disp(n);

A {1, 2, 3}

B Error: Cannot convert cell array to numeric array

C [1 2 3]

D ["1" "2" "3"]

💡 Hint

str2double converts each string in the cell array to a number.

str2double converts each string element in the cell array to a numeric value, resulting in a numeric array [1 2 3].

❓ Predict Output

expert

Output of converting mixed numeric types to single precision

What is the output of this MATLAB code?

MATLAB

a = int16(1000);
b = double(a);
c = single(b);
disp(class(c));

A double

B Error: Invalid conversion

C int16

D single

💡 Hint

int16 to double to single changes the class accordingly.

int16 value 1000 converts to double 1000, then to single 1000. disp(class(c)) prints 'single'.

Practice

1. Which MATLAB function converts a string representing a number into a numeric double type?

easy

A. str2double

B. double

C. int32

D. char

Solution

1. Step 1: Understand the input and output types

   The input is a string representing a number, and the output should be a numeric double type.

2. Step 2: Identify the correct conversion function

   str2double converts strings to double numbers, while double converts numeric types to double, int32 converts to 32-bit integers, and char converts numbers to characters.

3. Final Answer:

   str2double -> Option A

4. Quick Check:

   String to double = str2double [OK]

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

Common Mistakes:

• Using double on a string causes error
• Using int32 converts to integer, not double
• Using char converts to characters, not numbers

2. Which of the following is the correct syntax to convert a numeric variable x to a 32-bit integer in MATLAB?

easy

A. convertToInt32(x)

B. int(x, 32)

C. int32(x)

D. toInt32(x)

Solution

1. Step 1: Recall MATLAB's type conversion syntax

   MATLAB uses functions named after the target type, like int32, called with parentheses around the variable.

2. Step 2: Check each option's syntax

   Only int32(x) is valid MATLAB syntax. The others are not MATLAB functions or use incorrect syntax.

3. Final Answer:

   int32(x) -> Option C

4. Quick Check:

   Correct syntax for int32 conversion = int32(x) [OK]

Hint: Use function name with parentheses for conversion [OK]

Common Mistakes:

• Using non-existent functions like convertToInt32
• Incorrect function call syntax
• Confusing with other language syntax

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

x = '123.45';
y = str2double(x);
z = int32(y);
disp(z);

medium

A. 123.45

B. '123.45'

C. Error

D. 123

Solution

1. Step 1: Convert string to double

   str2double('123.45') converts the string to numeric double 123.45.

2. Step 2: Convert double to int32

   int32(123.45) converts the double to integer by truncating the decimal part, resulting in 123.

3. Final Answer:

   123 -> Option D

4. Quick Check:

   str2double + int32 truncates decimals = 123 [OK]

Hint: int32 truncates decimals after str2double [OK]

Common Mistakes:

• Expecting int32 to round instead of truncate
• Thinking str2double returns string
• Confusing output with original string

4. Identify the error in this MATLAB code snippet:

x = 65;
y = str2double(x);
disp(y);

medium

A. str2double cannot convert numeric input

B. x should be a string for str2double

C. Missing semicolon after disp(y)

D. disp cannot display numeric values

Solution

1. Step 1: Check input type for str2double

   str2double expects a string input, but x is numeric (65).

2. Step 2: Identify the cause of error

   Passing numeric x to str2double causes unexpected behavior or error because it is not a string.

3. Final Answer:

   x should be a string for str2double -> Option B

4. Quick Check:

   str2double needs string input [OK]

Hint: str2double requires string input, not numeric [OK]

Common Mistakes:

• Passing numeric directly to str2double
• Thinking disp needs semicolon
• Believing disp can't show numbers

5. You have a cell array of strings representing numbers: data = {'10', '20.5', '30', '40.7'}. Which MATLAB code correctly converts all elements to a numeric array of doubles?

hard

A. numArray = cellfun(@str2double, data);

B. numArray = double(data);

C. numArray = int32(data);

D. numArray = str2double(data);

Solution

1. Step 1: Understand data type and conversion needed

   data is a cell array of strings; we want a numeric double array.

2. Step 2: Use cellfun with str2double

   cellfun(@str2double, data) applies str2double to each cell element, converting strings to doubles.

3. Step 3: Check other options

   double(data) and int32(data) do not work on cell arrays directly; str2double(data) expects a string, not a cell array.

4. Final Answer:

   numArray = cellfun(@str2double, data); -> Option A

5. Quick Check:

   Use cellfun with str2double for cell string arrays [OK]

Hint: Use cellfun(@str2double, cellArray) for cell string to numbers [OK]

Common Mistakes:

• Trying double or int32 on cell arrays directly
• Using str2double on cell array without cellfun
• Not converting strings inside cells individually