CS 1101 Unit 3 Programming Assignment | Computer Science Coding Practice and Solutions

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CS 1101 – Unit 3 Programming Assignment
Benjamin Ifeoluwa Adebayo
University of the People
CS 1001 - Programming Fundamentals
1st December, 2025



Part 1: Countdown and Countup Recursive Functions

Explanation of the Code

This program explores the concept of recursion, where a function calls itself to solve a problem.
The assignment requires two recursive functions:

1. countdown(n): Given in the text, this function prints a number and calls itself with n-1
until it reaches 0.
2. countup(n): This new function accepts a negative number. It prints the number and calls
itself with n+1 (incrementing toward zero) until the base case is reached.

The program creates a decision control process using conditional execution. It accepts user input;
if the number is positive, it triggers countdown; if negative, it triggers countup.

Choice for Zero

For an input of zero, I chose to call the countdown function. Logically, "Blastoff!" represents the
end of a countdown timer. Since 0 implies no time is remaining, triggering the completion message
immediately via countdown is the most semantic choice.

Python Code for Part 1

# Function to count down from a positive number
def countdown(n):
if n <= 0:
print('Blastoff!')
else:
print(n)
countdown(n - 1)

# Function to count up from a negative number
def countup(n):
if n >= 0:
print('Blastoff!')
else:
print(n)
countup(n + 1)




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# Main program logic
def start_program():
# Getting input from the user
user_input = input("Please enter a number: ")

# Converting string input to integer
try:
n = int(user_input)

if n > 0:
print("Counting down:")
countdown(n)
elif n < 0:
print("Counting up:")
countup(n)
else:
# Choice for zero: calling countdown to signal immediate completion
print("Input is zero:")
countdown(n)

except ValueError:
print("Please enter a valid integer.")

# Call the function to run the program
start_program()




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