Learning to Solve Problems

Learning to Solve Problems#

Note

Source: Adapted from the C# edition (data/learning-to-problem-solve.rst). The six-step framework and bill-splitting example are Python translations of the original.

Programming is fundamentally about problem solving. The computer is a tool; the skill is figuring out how to express a solution in a way the computer can execute.

A Framework for Problem Solving#

When you encounter a new problem, work through these steps:

  1. Understand the problem. What are the inputs? What is the expected output? Work through a specific example by hand before writing any code.

  2. Identify the data. What values do you need to store? What types should they be? Give them meaningful names.

  3. Break it into steps. A program that calculates paint requirements needs to: read the room dimensions, calculate wall area, calculate ceiling area, and print the results. Each step is simple; together they solve the problem.

  4. Write the code. Translate each step into Python. Start with the simplest version that works.

  5. Test. Run the program with inputs you can check by hand. Try edge cases: what if one dimension is zero? What if the user types something that is not a number?

  6. Refine. Clean up names, add comments where the logic is non-obvious, and look for anything that could break.

The Data-in, Calculate, Data-out Pattern#

Many programs follow a simple pattern:

1. Get data from the user (or a file)
2. Perform calculations
3. Output the results

The painting program from A Sample Python Program follows this pattern exactly. So do most of the early programs in this book. Recognizing the pattern helps you organize your thinking.

Worked Example: Splitting a Bill#

Problem: A group of friends had dinner and want to split the bill evenly, including a 20% tip.

Step 1 — Understand the problem. Inputs: total bill amount, number of people. Output: amount each person owes.

Step 2 — Work through an example by hand. Bill = $80, people = 4. Tip = 20% of $80 = $16. Total = $80 + $16 = $96. Per person = $96 / 4 = $24.

Step 3 — Write the code:

bill = float(input("Enter the bill amount: $"))
people = int(input("How many people? "))

tip = bill * 0.20
total = bill + tip
per_person = total / people

print(f"Each person owes ${per_person:.2f}.")

Step 4 — Test. With bill = 80 and people = 4, the output should be Each person owes $24.00.

Notice how closely the code matches the hand calculation. Programming at its best is translating a clear solution into clear code.

Getting Unstuck#

Everyone gets stuck. A few strategies that help:

  • Print intermediate values. Add print() statements to see what your variables hold at each step.

  • Simplify. Remove parts of the program until it works, then add them back.

  • Read the error message. Python’s errors are informative — read them carefully, starting from the bottom.

  • Step away. A short break often lets you see the problem with fresh eyes.