Writing Algorithms - Flow Diagrams

Introduction to Flow Diagrams

A flow diagram (or flowchart) is another way to express algorithms, providing a visual representation of the logic within a program.
They use a set of specific symbols connected by arrows to denote flow of execution.
Flow diagrams can make understanding complex algorithms easier by showing each step precisely, including decisions (if statements), loops, and process steps.
They serve the same purpose as pseudocode, but are better at showcasing the flow of an algorithm.

Ovals represent the start and the end of the process.
Rectangles indicate a process or action to be carried out.
Diamond-shaped symbols represent decision points, involving a yes/no question or true/false test.
Arrows indicate the flow of control, showing the direction of the process.
Parallelograms often represent Input or Output operations.

Begin by identifying the start and end points of the process. These will be your oval symbols.
For each step in your process, use a rectangle. This could be a single operation (like ‘Increment counter’) or multiple (like ‘Calculate sum and average’).
Use diamonds to illustrate decisions within the algorithm, such as an if or else decision. Write the decision or condition to be tested inside the diamond.
Connect the symbols with arrows to show the flow of the algorithm. This should accurately represent all possible paths from start to finish.
Make sure your flow diagram follows a logical order and doesn’t have any breaks in the sequence.

As with pseudocode, use decomposition to break down complex problems into manageable sections.
Each sub-program can be represented as its own flowchart.
Large flowcharts can be broken down into smaller sub-processes, with a simple rectangle linking to another flowchart.

Always check the logic and the flow - does the flowchart accurately represent the problem and solve it correctly?
Could the flowchart be optimised or made more efficient? Look for repeated patterns or ways to simplify the logic.
As long as the flowchart can be understood by another person, you’ve achieved your goal! Remember, flow diagrams are about helping us think through our algorithms in a visual way.