Drawing Flowcharts

Drawing a flowchart means turning an algorithm into a clear visual diagram using the correct symbols, decision paths, and loop structures. A well-drawn flowchart communicates logic better than code alone.

Knowing the symbols is only the first step. Drawing a flowchart that clearly communicates an algorithm takes practice and a few key techniques. A good flowchart should be easy to follow from START to END, with arrows that never leave the reader guessing.

The Golden Rules of Drawing Flowcharts

Start and end with terminals — every flowchart needs a START and at least one END.
Use the correct symbol for each step — mixing up process and I/O shapes confuses readers.
Label every decision path — always mark the Yes and No branches of a diamond.
Flow generally top-to-bottom — this is the natural reading direction; exceptions (like loop arrows) should be clearly visible.
Arrows must always have arrowheads — direction matters.

Drawing a Sequence Algorithm

Task: calculate the area of a rectangle.

    ╭─────────╮
    │  START  │
    ╰────┬────╯
         ↓
    ╱────────────╲
   ╱ INPUT width  ╲
   ╲              ╱
    ╲────────────╱
         ↓
    ╱─────────────╲
   ╱ INPUT height  ╲
   ╲               ╱
    ╲─────────────╱
         ↓
    ┌──────────────────────┐
    │ SET area ← width × height │
    └──────────┬───────────┘
               ↓
    ╱──────────────────╲
   ╱  OUTPUT "Area:" + area ╲
   ╲                        ╱
    ╲──────────────────────╱
               ↓
    ╭─────────╮
    │   END   │
    ╰─────────╯

Drawing Selection (IF Statement)

Task: display "Pass" or "Fail" based on a score.

The decision diamond has one entry arrow and two exit arrows labelled Yes and No:

         ↓
    ╱────────────╲
   ╱ INPUT score  ╲
   ╲              ╱
    ╲────────────╱
         ↓
    ◇─────────────────────◇
    │   Is score ≥ 50?    │
    ◇─────────────────────◇
      Yes ↓         No ↓
  ┌──────────┐   ┌──────────┐
  │OUTPUT    │   │ OUTPUT   │
  │ "Pass"   │   │  "Fail"  │
  └────┬─────┘   └────┬─────┘
       └──────┬────────┘
              ↓
         ╭─────────╮
         │   END   │
         ╰─────────╯

Note

Notice how both branches from the diamond eventually merge before the END. When drawing multiple paths, merge them cleanly using a joining point — this keeps the diagram readable.

Drawing a Loop

Loops are shown by drawing an arrow that goes backwards up the diagram. This is the main exception to the top-to-bottom rule.

Task: count down from 5 to 1.

         ↓
    ┌──────────────┐
    │ SET n ← 5   │
    └──────┬───────┘
           ↓
    ◇──────────────────◇ ←──────────────┐
    │    Is n > 0?     │                 │
    ◇──────────────────◇                 │
      Yes ↓        No ↓                  │
  ╱──────────╲    ╭─────╮   ┌──────────┐ │
 ╱ OUTPUT n   ╲   │ END │   │SET n←n-1 │ │
 ╲             ╱  ╰─────╯   └─────┬────┘ │
  ╲───────────╱                   └───────┘
       ↓
  ┌──────────┐
  │SET n←n-1 │
  └────┬─────┘
       └──────→ (back up to condition diamond)

Tip

When drawing a loop, clearly show where the backwards arrow re-enters the diagram — usually at the decision diamond. Use a slight curve or an explicit junction dot to make it obvious.

Common Mistakes to Avoid

Mistake	Fix
Unlabelled decision arrows	Always write Yes/No on both paths
Missing START or END terminal	Add them — they are mandatory
Arrows with no arrowhead	Add arrowheads to show direction
Dead-end paths that never reach END	Every path must lead to an END
Using rectangles for input/output	Use parallelograms instead

Warning

A decision diamond with only one exit arrow is a logic error. A condition is always either True or False — both outcomes must have a defined path in your flowchart.

Practice Problems

List the shapes (in order) you would use to draw a flowchart for: start, ask the user for a number, check if the number is even, output 'even' or 'odd', then end.

Show answer

Terminal (START) → Parallelogram (INPUT number) → Diamond (Is number MOD 2 = 0?) → two branches: Parallelogram (OUTPUT 'even') and Parallelogram (OUTPUT 'odd') → both paths merge → Terminal (END).

A student draws a flowchart with a decision diamond but only draws one exit arrow. What is wrong and how do they fix it?

Show answer

A decision has exactly two outcomes (Yes and No), so it must have two exit arrows, each labelled clearly. The fix is to add the missing arrow for the other outcome and label both arrows as Yes and No.