Docs

Topic 7 · Algorithm design and problem-solving

The program development life cycle

Analysis, design, coding, and testing, and how decomposition and structure diagrams break a big problem into small ones.

Lesson 1 of 5Syllabus 7.1–7.3updated October 31, 2026

Four stages

Programs are built in stages. Each stage feeds the next, and testing often sends you back to fix the design or code.

  1. 1
    Analysis
    Understand the problem: abstraction, decomposition, and a list of requirements.
  2. 2
    Design
    Plan the solution with structure diagrams, flowcharts, and pseudocode.
  3. 3
    Coding
    Write the program, testing each part as you go (iterative testing).
  4. 4
    Testing
    Run the finished program with test data to check it works as required.

Abstraction and decomposition

Abstraction means keeping only the details that matter and ignoring the rest. A train map shows the stations and the order of stops, not the exact bends of the track.

Decomposition means breaking a problem into smaller sub-problems that are easier to solve, until each one is simple enough to code. Every computer system is made of sub-systems, which are made of further sub-systems.

When you decompose a problem, identify its inputs, processes, outputs, and storage.

Structure diagrams

A structure diagram shows decomposition as a tree. The whole system sits at the top, and each level below breaks a box into smaller parts.

Structure diagram for an alarm clock app
  • Alarm clock
    • Set alarm
      • Input time
      • Save time
    • Check time
      • Read clock
      • Compare
    • Ring alarm
      • Play sound
      • Snooze

Ways to design an algorithm

An algorithm is a set of steps that solves a problem. You can write the same algorithm in three ways:

  • Structure diagram: shows how the problem is broken down, but not the order of steps.
  • Flowchart: shows the steps and decisions as connected shapes.
  • Pseudocode: a structured, language-neutral way to write the steps, close to real code.

Exam tip. Next: the flowcharts lesson shows every flowchart symbol. The programming topic covers pseudocode in detail.

Key terms

Abstraction
Removing unnecessary details to focus on what matters.
Decomposition
Breaking a problem into smaller sub-problems.
Structure diagram
A tree diagram showing how a system is broken into sub-systems.
Algorithm
A sequence of steps to solve a problem.

Check yourself

Name the four stages of the program development life cycle.Show answer

Analysis, design, coding, testing.

In which stage are structure diagrams and flowcharts produced?Show answer

Design.

What is the difference between abstraction and decomposition?Show answer

Abstraction removes unnecessary detail. Decomposition breaks the problem into smaller parts.

Try it in the editor PracticeOpen manual