Turning algorithms in words and flowcharts into Python

Matching symbols to code (spec 10.2.1)

Spotting loops in a flowchart

If an arrow goes back to a decision above the steps, the test is made first: a while loop. If the steps come first and the decision afterwards loops back, the body runs at least once: in Python, set up the condition so the loop is entered the first time (for example with a flag or by doing the first input before the loop).

Worked translation

Algorithm in words: 'Set count to 0. Input a number. While the number is not -1: if it is even, add 1 to count; input the next number. Output count.'

count = 0
number = int(input())
while number != -1:
    if number % 2 == 0:
        count = count + 1
    number = int(input())
print(count)

With inputs 4, 7, 10, -1 the output is 2. The value -1 is a rogue value (sentinel): it ends the input and is not processed.

Worked example

Translate: 'Repeat 5 times: input a temperature; if it is above the highest so far, store it. Then output the highest.'

1. Fixed number of repeats: for i in range(5):
2. Initialise highest before the loop: highest = None, or the first value
3. Decision inside the loop: if highest is None or temp > highest: highest = temp
4. Output after the loop: print(highest)

Answer: for loop, if inside it, print after it

Check yourself

1. Which Python construct does a diamond in a flowchart usually become?
   • A print statement
   • An assignment
   • An if statement or a loop condition
   • An import statement
   Show answer

   An if statement or a loop condition. A diamond is a decision with yes and no exits.

2. A flowchart box says 'Output total'. Which shape should it be?
   • Parallelogram
   • Diamond
   • Rectangle
   • Rounded rectangle
   Show answer

   Parallelogram. Input and output use a parallelogram.

3. The user types 5, 8, 2, 0 and 9. What is displayed? ```python total = 0 value = int(input()) while value != 0: total = total + value value = int(input()) print(total) ```
   Show answer

   15. The rogue value 0 ends the loop and is not added: 5 + 8 + 2 = 15.

4. This code follows the algorithm 'Set n to 6 and result to 1. While n is greater than 0, double result and subtract 2 from n. Output result.' What is displayed? ```python n = 6 result = 1 while n > 0: result = result * 2 n = n - 2 print(result) ```
   Show answer

   8. The loop runs for n = 6, 4, 2: three doublings, giving 8.

5. Algorithm: 'For each mark in the list, if the mark is at least 50 add 1 to passes. Output passes.' Which line completes the code? ```python marks = [45, 50, 72, 38, 66] passes = 0 for mark in marks: __________ passes = passes + 1 print(passes) ```
   • `if mark > 50:`
   • `while mark >= 50:`
   • `if marks >= 50:`
   • `if mark >= 50:`
   Show answer

   `if mark >= 50:`. 'At least 50' means >= 50, giving 50, 72 and 66: 3 passes.

6. In a flowchart, the steps 'Input password' and 'Add 1 to attempts' come first, then a decision 'Correct?' with the No arrow going back to the input. What does this show?
   • A loop that may run zero times
   • A loop whose body always runs at least once
   • A selection with no loop
   • A count-controlled loop of fixed length
   Show answer

   A loop whose body always runs at least once. The test comes after the body, so the body runs before the first check.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Computer Science specification (XCP01/YCP01), first teaching 2026
• Pearson IAL Computer Science Unit 2 Programming Language Subset (PLS), Python 3
• Pearson IAL Computer Science IAS sample assessment materials (Unit 2 paper and mark scheme)

Last updated 8 November 2026. Spotted a mistake? Tell us.