Write pseudocode from a flowchart

9.2 Algorithms – Writing Pseudocode from a Flowchart

What is a Flowchart?

A flowchart is a visual diagram that shows the steps of an algorithm. Think of it like a recipe card for a computer: each shape is a cooking step, and the arrows are the order in which you follow them. 🍰

Common Flowchart Symbols

Translating Symbols to Pseudocode

1. Identify the Start symbol and write START.
2. For each Process rectangle, write the action in plain English, e.g., SET sum = sum + value.
3. When you hit a Decision diamond, translate it into an IF statement. Remember the two possible paths: THEN and ELSE.
4. Use READ for input and WRITE for output.
5. Finish with the End symbol and write END.

Example: Sorting Numbers (Bubble Sort)

Let’s walk through a simple flowchart for Bubble Sort and write the pseudocode. Imagine you have a list of numbers that need to be sorted from smallest to largest.

1. Start
2. Read the list of numbers into array $A$.
3. Set n = length(A).
4. FOR i = 1 TO n-1 DO
5.  FOR j = 1 TO n-i DO
6.   IF A[j] > A[j+1] THEN
7.    SWAP A[j] and A[j+1]
8.   END IF
9.  END FOR
10. END FOR
11. Write the sorted list.
12. End

Practice Exercise

Below is a simple flowchart (described in words). Translate it into pseudocode. Use the symbols table as your guide.

• Start
• Read integer n.
• Set sum = 0.
• FOR i = 1 TO n DO
•  READ integer x.
•  SET sum = sum + x.
• END FOR
• Write sum.
• End

Try writing it out, then compare with the answer below.

1. START
2. READ n
3. SET sum = 0
4. FOR i = 1 TO n DO
5.  READ x
6.  SET sum = sum + x
7. END FOR
8. WRITE sum
9. END