Functions (reusable code blocks) in Intro to Computing - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a function in programming?

A function is a reusable block of code that performs a specific task. It helps avoid repeating the same code and makes programs easier to read and maintain.

beginner

Why do we use functions in programming?

Functions help by breaking a program into smaller parts, making it easier to understand, reuse, and test. They save time by avoiding repeated code.

beginner

What is the difference between a function definition and a function call?

A function definition is where you write the code for the function. A function call is when you use or run the function in your program.

intermediate

Explain the concept of input and output in functions.

Functions can take inputs (called parameters) to work with different data. They can also give back results (called return values) after processing.

beginner

How can you think of a function using a real-life analogy?

Think of a function like a coffee machine: you put in coffee beans and water (inputs), press a button (call the function), and get coffee (output). You can use the machine many times without making coffee from scratch each time.

What does a function do in a program?

A Stores data permanently

B Performs a specific task when called

C Repeats the same code multiple times

D Deletes parts of the program

A function performs a specific task when called, helping to organize and reuse code.

Which of these is a function call?

A greet()

B function greet

C def greet():

D return greet

greet() is a function call that runs the code inside the function named greet.

What do we call the values given to a function to work with?

A Variables

B Returns

C Loops

D Parameters

Parameters are the inputs given to a function to process.

Why is using functions helpful?

A It helps reuse code and organize programs

B It hides errors completely

C It slows down the program

D It makes the program longer

Functions help reuse code and organize programs, making them easier to manage.

What is the output of a function?

A The code inside the function

B The name of the function

C The result the function gives back after running

D The input values

The output is the result the function returns after processing the inputs.

Explain what a function is and why it is useful in programming.

Think about how functions help you write less code and keep things organized.

Describe the difference between a function definition and a function call with an example.

One is where you write the code, the other is when you use it.

Practice

1. What is the main purpose of a function in programming?

easy

A. To display output on the screen

B. To reuse a block of code multiple times

C. To store data permanently

D. To create a new variable

Solution

1. Step 1: Understand what a function does

   A function is a reusable block of code designed to perform a specific task.

2. Step 2: Identify the main purpose

   Functions help avoid repeating the same code by allowing reuse whenever needed.

3. Final Answer:

   To reuse a block of code multiple times -> Option B

4. Quick Check:

   Function purpose = reuse code [OK]

Hint: Functions help reuse code blocks easily [OK]

Common Mistakes:

• Confusing functions with variables
• Thinking functions store data permanently
• Believing functions only display output

2. Which of the following is the correct way to define a function named greet that takes no inputs?

easy

A. function greet() {}

B. function greet:

C. def greet()

D. def greet():

Solution

1. Step 1: Recognize Python function syntax

   In Python, functions are defined using the keyword def, followed by the function name and parentheses with parameters (empty if none), ending with a colon.

2. Step 2: Check each option

   def greet(): matches Python syntax. function greet() {} and function greet: use JavaScript style or incorrect syntax. def greet() misses the colon.

3. Final Answer:

   def greet(): -> Option D

4. Quick Check:

   Python function = def name(): [OK]

Hint: Python functions start with def and end with colon [OK]

Common Mistakes:

• Omitting the colon at the end
• Using JavaScript syntax in Python
• Leaving out parentheses

3. What will be the output of this code?

def add(x, y):
    return x + y

result = add(3, 4)
print(result)

medium

A. TypeError

B. 34

C. 7

D. None

Solution

1. Step 1: Understand the function call

   The function add takes two inputs x and y and returns their sum.

2. Step 2: Calculate the return value

   Calling add(3, 4) returns 3 + 4 = 7, which is stored in result. Printing result outputs 7.

3. Final Answer:

   7 -> Option C

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Add numbers inside function returns their sum [OK]

Common Mistakes:

• Thinking it concatenates numbers as strings
• Expecting a TypeError due to missing return
• Assuming print shows None

4. Identify the error in this function definition:

def multiply(a, b)
    return a * b

medium

A. Missing colon after function header

B. Incorrect return statement

C. Function name is invalid

D. Parameters should be in square brackets

Solution

1. Step 1: Check function header syntax

   In Python, the function header must end with a colon (:). Here, it is missing after def multiply(a, b).

2. Step 2: Verify other parts

   The return statement and function name are correct. Parameters use parentheses, not square brackets.

3. Final Answer:

   Missing colon after function header -> Option A

4. Quick Check:

   Function header ends with : [OK]

Hint: Function headers always end with a colon in Python [OK]

Common Mistakes:

• Forgetting the colon at the end
• Using square brackets for parameters
• Misnaming the function

5. You want to create a function that returns the square of a number only if the number is positive; otherwise, it returns zero. Which function correctly implements this?

hard

A. def square_if_positive(n):
if n > 0:
return n * n
else:
return 0

B. def square_if_positive(n):
if n >= 0:
return n ** 2
else:
return n

C. def square_if_positive(n):
return n * n if n > 0 else None

D. def square_if_positive(n):
if n < 0:
return n * n
else:
return 0

Solution

1. Step 1: Understand the condition

   The function should return the square of n only if n is positive (greater than 0). Otherwise, it returns 0.

2. Step 2: Check each option

   def square_if_positive(n): if n > 0: return n * n else: return 0 correctly checks n > 0 and returns n * n, else 0. def square_if_positive(n): if n >= 0: return n ** 2 else: return n includes zero as positive and returns n if negative, which is incorrect. def square_if_positive(n): return n * n if n > 0 else None returns None instead of 0 when n is not positive. def square_if_positive(n): if n < 0: return n * n else: return 0 squares negative numbers and returns 0 otherwise, which is opposite.

3. Final Answer:

   def square_if_positive(n): if n > 0: return n * n else: return 0 -> Option A

4. Quick Check:

   Positive n squared, else zero [OK]

Hint: Check condition n > 0, return square else zero [OK]

Common Mistakes:

• Including zero as positive
• Returning None instead of zero
• Reversing the condition logic