Local functions in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a local function named 'square' that returns the square of input 'x'.

MATLAB

function y = main()
    y = square(5);
end

function result = [1](num)
    result = num^2;
end

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

Apower

Bmultiply

Ccube

Dsquare

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different function name than the one called in main.

Forgetting to define the local function after the main function.

The local function must be named 'square' to match the call in the main function.

2fill in blank

medium

Complete the code to call the local function 'greet' inside the main function.

MATLAB

function main()
    message = [1]('Alice');
    disp(message);
end

function msg = greet(name)
    msg = ['Hello, ' name '!'];
end

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

Agreet

Bhello

CsayHello

Dwelcome

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a function name that does not exist.

Using a different case or spelling for the function name.

The local function is named 'greet', so the call must use 'greet'.

3fill in blank

hard

Fix the error in the local function definition by completing the function header correctly.

MATLAB

function output = main()
    output = addFive(10);
end

function result = [1](x)
    result = x + 5;
end

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

AAddfive

BaddFive

Caddfive

Dadd_Five

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect capitalization in the function name.

Adding underscores or changing spelling.

The function name must exactly match the call in main, which is 'addFive'.

4fill in blank

hard

Fill both blanks to create a local function 'multiply' that multiplies two inputs 'a' and 'b'.

MATLAB

function result = main()
    product = multiply(3, 4);
    disp(product);
end

function [1] = [2](a, b)
    [1] = a * b;
end

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

Aresult

Boutput

Cmultiply

Dprod

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the function or output variable than in the call.

Mixing up the order of output variable and function name.

The function output variable is 'result' and the function name is 'multiply' to match the call.

5fill in blank

hard

Fill all three blanks to create a local function 'concatStrings' that joins two strings with a space.

MATLAB

function result = main()
    combined = concatStrings('Hello', 'World');
    disp(combined);
end

function [1] = [2](str1, str2)
    [1] = [str1 [3] str2];
end

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

Aresult

BconcatStrings

C' '

Dstrcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong function name or output variable.

Forgetting to add the space between strings.

Using 'strcat' instead of square brackets for concatenation.

The output variable is 'result', the function name is 'concatStrings', and the space character is ' ' to join the strings.

Practice

1. What is a key characteristic of a local function in MATLAB?

easy

A. It automatically runs when MATLAB starts.

B. It must be saved in a separate file with the same name.

C. It can only be called from the command window.

D. It is defined inside the same file as the main function or script.

Solution

1. Step 1: Understand local function placement

   Local functions are defined inside the same file as the main function or script, not separately.

2. Step 2: Compare with other options

   Options A, B, and C describe behaviors that do not match local functions in MATLAB.

3. Final Answer:

   It is defined inside the same file as the main function or script. -> Option D

4. Quick Check:

   Local function location = same file [OK]

Hint: Local functions live inside the main file, not separate files. [OK]

Common Mistakes:

• Thinking local functions need separate files
• Believing local functions run automatically
• Assuming local functions can only be called from command window

2. Which of the following is the correct way to define a local function inside a MATLAB script file?

easy

A. def localFunc(x):
return x^2

B. localFunc(x) = x^2;

C. function y = localFunc(x)
y = x^2;
end

D. function y = localFunc(x)
y = x^2;

Solution

1. Step 1: Identify MATLAB function syntax

   MATLAB local functions start with the keyword function, followed by output, name, and input, and end with end.

2. Step 2: Check each option

   function y = localFunc(x) y = x^2; end uses correct MATLAB syntax with function and end. def localFunc(x): return x^2 is Python syntax. localFunc(x) = x^2; is invalid MATLAB syntax. function y = localFunc(x) y = x^2; misses the end keyword.

3. Final Answer:

   function y = localFunc(x) y = x^2; end -> Option C

4. Quick Check:

   MATLAB function syntax = function y = localFunc(x) y = x^2; end [OK]

Hint: MATLAB functions need 'function' and 'end' keywords. [OK]

Common Mistakes:

• Omitting the 'end' keyword
• Using Python or other language syntax
• Trying to assign function like a variable

3. Consider this MATLAB code in a file named mainFile.m:

function result = mainFile(x)
  result = squarePlusOne(x);

  function y = squarePlusOne(n)
    y = n^2 + 1;
  end
end

What is the return value of mainFile(3)?

medium

A. 10

B. 9

C. 7

D. Error: undefined function

Solution

1. Step 1: Understand the local function call

   The main function calls squarePlusOne(3). The local function computes 3^2 + 1 = 9 + 1 = 10.

2. Step 2: Confirm output assignment

   The result from the local function is assigned to result, which is returned by mainFile. So mainFile(3) returns 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   3 squared plus 1 = 10 [OK]

Hint: Calculate local function output then return it. [OK]

Common Mistakes:

• Forgetting to add 1 after squaring
• Thinking local functions are inaccessible
• Confusing variable names

4. This MATLAB script contains a local function:

function output = calc(x)
  output = doubleValue(x);

  function y = doubleValue(n)
    y = n * 2
  end

result = calc(5);

What is the error in this code?

medium

A. Missing semicolon after y = n * 2 in local function

B. Missing end keyword for the main function calc

C. Local function doubleValue is not accessible inside calc

D. Local functions cannot return values

Solution

1. Step 1: Check function endings

   The local function doubleValue has an end, but the main function calc does not have its own end keyword.

2. Step 2: Verify MATLAB syntax rules

   Each function in MATLAB must end with end. Missing end for calc causes a syntax error.

3. Final Answer:

   Missing end keyword for the main function calc -> Option B

4. Quick Check:

   Every function needs 'end' [OK]

Hint: Count 'end' keywords: one per function needed. [OK]

Common Mistakes:

• Assuming semicolon omission causes error
• Thinking local functions are inaccessible
• Believing local functions can't return values

5. You want to write a MATLAB function that computes the factorial of a number using a local helper function to multiply numbers recursively. Which of the following code snippets correctly uses a local function for this purpose?

hard

A. function f = factorialMain(n)
f = helper(n);
function val = helper(k)
if k <= 1
val = 1;
else
val = k * helper(k-1);
end
end
end

B. function f = factorialMain(n)
f = helper(n);
end
function val = helper(k)
if k <= 1
val = 1;
else
val = k * helper(k-1);
end

C. function f = factorialMain(n)
f = factorial(n);
function val = helper(k)
val = k * helper(k-1);
end
end

D. function f = factorialMain(n)
f = n * factorialMain(n-1);
end

Solution

1. Step 1: Identify correct local function usage

   function f = factorialMain(n) f = helper(n); function val = helper(k) if k <= 1 val = 1; else val = k * helper(k-1); end end end defines the local function helper inside factorialMain and uses recursion properly with base case.

2. Step 2: Check other options for errors

   function f = factorialMain(n) f = helper(n); end function val = helper(k) if k <= 1 val = 1; else val = k * helper(k-1); end defines helper outside main function (not local). function f = factorialMain(n) f = factorial(n); function val = helper(k) val = k * helper(k-1); end end calls factorial (built-in) and has incomplete helper. function f = factorialMain(n) f = n * factorialMain(n-1); end is a recursive main function but lacks base case and local function.

3. Final Answer:

   function f = factorialMain(n) f = helper(n); function val = helper(k) if k <= 1 val = 1; else val = k * helper(k-1); end end end -> Option A

4. Quick Check:

   Local recursive helper inside main function = function f = factorialMain(n) f = helper(n); function val = helper(k) if k <= 1 val = 1; else val = k * helper(k-1); end end end [OK]

Hint: Local functions go inside main function with 'function' and 'end'. [OK]

Common Mistakes:

• Defining helper function outside main function
• Missing base case in recursion
• Calling built-in factorial instead of local helper