A flowchart only works if everyone reads the symbols the same way. That is why the symbols are standard: a diamond always means a decision, whoever draws it.
Standard symbols
| Symbol | Name | Use |
|---|---|---|
| Oval (rounded rectangle) | Terminator | Start and Stop |
| Rectangle | Process | Calculations and assignments, for example total = total + i |
| Parallelogram | Input/Output | Read a value or display a result |
| Diamond | Decision | A yes/no question with two exits |
| Arrow | Flow line | Shows the direction of flow |
| Small circle | Connector | Joins parts of a chart or continues on another page |
What goes inside each symbol
- Terminator (oval): only the words Start or Stop (or Begin/End). A flowchart has exactly one Start.
- Process (rectangle): an action that changes data, written as an assignment such as
total = total + iorarea = length * width. You can put several closely related assignments in one box. - Input/Output (parallelogram): begin the text with Read or Input for input, and Display, Print or Output for output, so the direction is clear.
- Decision (diamond): a question that can only be answered yes or no, such as
marks >= 50?. Never write an action such as "add 1" in a diamond. - Flow line (arrow): always add the arrow head, so the direction cannot be misread.
- Connector (small circle): contains a letter or number. Two connectors with the same label are the same point in the chart.
Rules for drawing flowcharts
- Use exactly one Start and at least one Stop.
- Flow from top to bottom and left to right.
- Every decision diamond has two labelled exits (Yes/No or True/False).
- Every process box has one entry and one exit.
- Do not cross flow lines; use connectors if needed.
- Keep text short and use the same variable names throughout.
The three structures as flowcharts
Each building block from 1.1.2 has its own shape in a flowchart:
- Sequence: process and input/output boxes in a straight line, one under another.
- Selection: a diamond with two exits (Yes and No). Each exit leads to its own boxes, and the two paths join again before the next common step.
- Iteration: a diamond whose Yes exit leads to the loop body, and an arrow from the end of the body goes back up to just before the diamond. The No exit leaves the loop.
You will see all three in the worked examples in 1.2.2.
How to read a flowchart
Put your finger on Start and follow the arrows. At each process box, write down the new value of each variable. At each diamond, work out the answer with the current values and follow that exit. Stop when you reach Stop. This is exactly a dry run, and it is how you check a flowchart before coding it.
Common mistakes: a decision with only one exit; arrows without heads; two Start symbols; an action written inside a diamond; a loop that has no way out; and lines that cross because the chart was not planned. Check every flowchart against the rules above before you hand it in.
Remember
- Oval for Start/Stop, rectangle for process, parallelogram for input/output, diamond for decisions.
- Every diamond has exactly two labelled exits.
- A loop is drawn as an arrow back to a point before the decision.