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AQA A Level 7517 Pseudo-code Runner

Run AQA A Level Computer Science 7517 pseudo-code online, with subroutines, arrays and string handling. Free, in your browser, no sign-up.

AQA 7517

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7517 pseudo-code rules

AQA A Level pseudo-code for algorithms such as searching, sorting, recursion and stacks.

Assign with ← (type <-); constants use CONSTANT NAME = value.
Zero-based arrays created with lists, e.g. items ← [3, 8, 15].
SUBROUTINE blocks that RETURN a value act as functions.
DIV and MOD are written between values, e.g. (low + high) DIV 2.

7517 example programs

Every example runs exactly as shown. Open one in the editor to change it and run it again.

Binary search

An iterative binary search SUBROUTINE that returns the index of the target or -1.

SearchingSubroutines

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# Iterative binary search on a sorted list
SUBROUTINE binarySearch(items, target)
  low ← 0
  high ← LEN(items) - 1
  WHILE low ≤ high
    mid ← (low + high) DIV 2
    IF items[mid] = target THEN
      RETURN mid
    ELSE IF items[mid] < target THEN
      low ← mid + 1
    ELSE
      high ← mid - 1
    ENDIF
  ENDWHILE
  RETURN -1
ENDSUBROUTINE

numbers ← [3, 8, 15, 21, 34, 42, 57]
OUTPUT binarySearch(numbers, 34)
OUTPUT binarySearch(numbers, 5)

Output: 4 -1

Recursive Fibonacci

A recursive SUBROUTINE with a base case generates the first eleven Fibonacci numbers.

RecursionSubroutines

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# Recursive Fibonacci
SUBROUTINE fib(n)
  IF n < 2 THEN
    RETURN n
  ENDIF
  RETURN fib(n - 1) + fib(n - 2)
ENDSUBROUTINE

FOR i ← 0 TO 10
  OUTPUT fib(i)
ENDFOR

Output: 0 1 1 2 3 5 8 13 21 34 55

Stack with push and pop

Implements a fixed-size stack with an array and a top pointer, including full and empty checks.

Data structuresSubroutinesArrays

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# A stack stored in an array
CONSTANT SIZE = 3
stack ← [0, 0, 0]
top ← -1

SUBROUTINE push(item)
  IF top = SIZE - 1 THEN
    OUTPUT 'Stack full, cannot push ' + INT_TO_STRING(item)
  ELSE
    top ← top + 1
    stack[top] ← item
  ENDIF
ENDSUBROUTINE

SUBROUTINE pop()
  IF top = -1 THEN
    OUTPUT 'Stack empty'
    RETURN -1
  ENDIF
  item ← stack[top]
  top ← top - 1
  RETURN item
ENDSUBROUTINE

push(5)
push(9)
push(2)
push(7)
OUTPUT pop()
OUTPUT pop()

Output: Stack full, cannot push 7 2 9

Bubble sort

Sorts a list in place with nested loops and a swapped flag.

SortingArraysLoops

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# Bubble sort with an early exit
items ← [29, 3, 17, 8, 42, 1]
n ← LEN(items)
swapped ← True
WHILE swapped
  swapped ← False
  FOR i ← 0 TO n - 2
    IF items[i] > items[i + 1] THEN
      temp ← items[i]
      items[i] ← items[i + 1]
      items[i + 1] ← temp
      swapped ← True
    ENDIF
  ENDFOR
  n ← n - 1
ENDWHILE
FOR item IN items
  OUTPUT item
ENDFOR

Output: 1 3 8 17 29 42

7517 pseudo-code rules

7517 example programs

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