Flowcharts for GCSE Computer Science

Representing algorithms for GCSE Computer Science

There are several ways to represent algorithms for GCSE Computer Science:

  • Structured English
  • Flowchart
  • Pseudocode
  • Program statements in a particular language

In this article we are looking at flowcharts for GCSE Computer Science.

For our example, we will create an algorithm which determines whether a given whole number is even or odd. The algorithm makes use of the MOD operator, which is represented in Python using the % sign. The principle is simple, but it can take some practice to get used to. MOD gives the remainder when dividing one integer by another. So for example:

  • 5 divided by 2 gives 2 remainder 1
  • 6 divided by 2 gives 3 remainder 0

Try running the Python code below to see how this pattern works when dividing by 2 and keeping the remainder.

for i in range(11):
    print(i % 2)


Modulo operator lesson

If you want to master the modulo operator, check out this complete lesson with worksheets and practice examples, including Python code solutions. [product id=4961]

Flowchart the Even/Odd Algorithm

The flowchart for this algorithms is shown below. Make sure you can follow it, understanding all the symbols used. There is a key for the symbols at the top of this article.

Flowcharts for GCSE Computer Science Even or Odd algorithm

You should copy this flowchart on paper now to help remember and understand it. I recommend practicing flowcharts with paper and pencil as well as using an online tool such as draw.io

Programming the Even/Odd Algorithm in Python

Have a go now at writing the Python code for this algorithm. The solution is available by clicking on “show solution” but have a good attempt for yourself first.

Flowchart practice exercise

Draw a flowchart for an algorithm which takes the base length of a square as input and prints the area of the square.

Good luck with mastering flowcharts for GCSE Computer Science.

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