Pseudocode

AQA 4.3.3 — Pseudocode

Retrieval: the previous lesson's number-guessing flowchart represents an algorithm visually. Pseudocode represents the exact same kind of algorithm as structured text — readable like a program, but without committing to any one language's exact syntax.

AQA-style pseudocode conventions

Construct	Pseudocode	Python equivalent
Assignment	`total ← 0`	`total = 0`
Selection	`IF x > 10 THEN ... ELSE ... ENDIF`	`if x > 10: ... else: ...`
Iteration (count-controlled)	`FOR i ← 1 TO 5 ... ENDFOR`	`for i in range(1, 6): ...`
Iteration (condition-controlled)	`WHILE x < 10 ... ENDWHILE`	`while x < 10: ...`
Input / output	`INPUT x`, `OUTPUT x`	`x = input()`, `print(x)`

Common mistake

Forgetting the closing keyword (ENDIF, ENDWHILE, ENDFOR) — in pseudocode, indentation alone isn't considered sufficient to show where a block ends, unlike Python. Also easy to mix up: pseudocode's ← for assignment is a different symbol from =, which in pseudocode (as in maths) means equality, not assignment.

Worked example — pseudocode to Python

temperature ← INPUT
IF temperature > 30 THEN
    OUTPUT "Hot"
ELSE IF temperature > 15 THEN
    OUTPUT "Mild"
ELSE
    OUTPUT "Cold"
ENDIF

Translated into Python:

temperature = int(input())
if temperature > 30:
    print("Hot")
elif temperature > 15:
    print("Mild")
else:
    print("Cold")

Trace it

Trace the pseudocode above (not the Python) for temperature = 22. Which branch executes, and what is output? (22 is not > 30, but is > 15, so the "Mild" branch executes and "Mild" is output.)

Translate it the other way

Take this Python and rewrite it as AQA-style pseudocode, using the conventions table above:

total = 0
count = 0
while count < 5:
    total = total + count
    count = count + 1
print(total)

Challenge

Write AQA-style pseudocode for a simple grade calculator (input a percentage; output "Pass" for 40 or above, "Fail" otherwise), then implement your own pseudocode in Python and confirm both versions agree on the same test inputs.

Looking ahead: every algorithm for the rest of this sequence (Linear Search onward) will be introduced as working Python directly — but the pseudocode-to-Python translation skill from this lesson is exactly what you'd use to answer an AQA exam question that gives you an algorithm in pseudocode form.

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