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)

Output:
0
1
0
1
0
1
0
1
0
1
0

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.

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.

# Even or odd?

num = int(input("Enter a whole number: "))

if num % 2 == 0:
    print(num, "is even")
else:
    print(num, "is odd.")

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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