Decomposition is a problem-solving technique used in computer science to break down complex problems into smaller, more manageable parts.

It involves dividing a problem into subproblems that are easier to understand, solve, and implement independently.

Reduced complexity

Decomposition allows us to tackle complex problems by breaking them down into simpler components.

Modularity

It promotes modular design, where each component performs a specific task, making it easier to understand and maintain.

Code reusability

Decomposed subproblems can be reused in different contexts, saving time and effort.

Efficient collaboration

Decomposition enables multiple programmers to work on different components simultaneously, enhancing productivity.

1, Define the problem

Clearly understand and define the problem that needs to be solved.

2. Break down the problem

Analyze the problem and break it down into smaller, manageable subproblems

3. Repeat for the subproblems

If the subproblem is still complex, break it down in further subproblems.

Comment-first coding means writing the steps of an algorithm as comments before writing any code. The comments become a plan, a bit like pseudocode inside the program.

• Break the task into small steps, one comment each.
• Check the plan makes sense before you start coding.
• Write the code for each comment underneath it.
• Keep the comments: they explain the program to the next person who reads it.

Task: find the average of the scores entered, stopping when the user types -1. Each comment is one sub-problem, so decomposing and coding happen in the same place. First the plan:

# Set total and count to 0
# Ask for a score
# While the score is not -1:
#     Add the score to total and 1 to count
#     Ask for the next score
# If count is more than 0, print total / count

Then the code goes under each comment:

# Set total and count to 0
total = 0
count = 0
# Ask for a score
score = int(input("Score: "))
# While the score is not -1:
while score != -1:
    # Add the score to total and 1 to count
    total = total + score
    count = count + 1
    # Ask for the next score
    score = int(input("Score: "))
# If count is more than 0, print total / count
if count > 0:
    print(total / count)

Entering 6, 8 and then -1 prints 7.0.