OCR GCSE Computer Science Exam Reference Language (J277): every command with examples

Formula sheet

The card below opens today's Computer Science paper with the language reference in the drawer, so you practise reading and writing code the way the paper presents it. The tables follow, in our own layout. The commands are those in OCR's specification section 3c, so check it before you rely on anything here. The specification does not say whether the language is printed as a sheet in the paper, so learn it as if it is not.

Operators

MOD gives the remainder after division and DIV gives the whole number quotient.

Variables, input and output

Iteration and selection

Strings

In .substring(x, i), x is the starting index and i is the number of characters. Strings are indexed from 0.

Files and arrays

Arrays are indexed from 0, so array colours[5] has indexes 0 to 4, and an array stores one data type.

Subprograms and random numbers

random(1, 6) gives a random integer from 1 to 6 inclusive, and random(-1.0, 10.0) gives a real number in that range.

Reading and writing ERL

Read the code from the top, one line at a time, and keep a table of the variables. Take this short program, which averages five marks:

total = 0
for i = 0 to 4
    mark = int(input("Enter mark"))
    total = total + mark
next i
average = total / 5
print("Average: " + str(average))

The loop runs for i = 0, 1, 2, 3 and 4, which is 5 times. Suppose the marks entered are 12, 15, 9, 18 and 6. Trace the variables line by line:

The program then prints the word Average followed by 12, because 60 / 5 = 12. The input function returns text, so the int() casting is needed before adding.

A function that returns a value

function isEven(n)
    if n MOD 2 == 0 then
        return true
    else
        return false
    endif
endfunction

print(isEven(17))

17 MOD 2 is 1, so the condition is false and the program prints false. A function returns a value, so store it in a variable or print it. A procedure does not return one.

What the reference does not give you

• How to choose the structure. It lists a for loop, a while loop and a do until loop. Which one a question needs is your decision.
• Algorithms. Searching, sorting and the other algorithms in the specification are not written out. You need to know how they work.
• Logic and design tools. Flowchart symbols, trace tables and the rest of the Component 2 skills sit outside the language reference.
• Every function of every language. If you answer in a high-level language, the reference does not cover its own syntax.
• Errors. It does not tell you what a syntax or logic error looks like, so learn to spot both.

How to use ERL in the exam

1. Read the whole program once before you trace it.
2. Make a table with a column for each variable, and fill in one row for each pass of a loop.
3. Remember that arrays and strings are indexed from 0.
4. In a "write" question use the exact keywords: endif, endwhile, next, endfunction.
5. Check boundary values: a for loop to 9 includes 9, and DIV and MOD behave differently from /.

ERL and other boards' languages

OCR's specification says answers in pseudocode, natural English or bullet points will not be awarded marks where a response must be in ERL or a high-level language. Other boards use their own language references,. If you sit AQA or Edexcel, use the language your board names.

The specification says Component 2 lasts 1 hour 30 minutes. For the boards, papers and grade boundaries, see our GCSE Computer Science guide.

Use the sheet with today's paper

Uni-Sine publishes a free daily paper for GCSE Computer Science. It is a short timed paper of 8 questions worth 25 to 35 marks, not a full OCR paper, and it is not written by OCR. Open the reference, set a timer and write the code you use at the top of each answer. After marking, look at any question where you used the wrong keyword or the wrong loop.

Common mistakes

• Off by one in a for loop. for i = 0 to 9 runs 10 times, from 0 to 9 inclusive.
• Mixing up MOD and DIV. MOD is the remainder and DIV is the whole number quotient.
• Forgetting to cast input. input() gives text, so use int() or float() before arithmetic.
• Counting arrays from 1. array colours[5] has indexes 0 to 4.
• Missing the end keyword. Every if has an endif, and every while has an endwhile.
• Using = to compare. Assignment is =, and comparison is ==.

Exam answers

The answers and a worked mark scheme come with today's paper once it is marked. Sit the paper with the sheet open beside you, mark it, and the worked answers show which line of the sheet each question wanted. We do not publish official or past paper answers.

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UK · GCSEOCR GCSE Computer Science (J277): papers and gradesOCR GCSE Computer Science (J277) explained: two 1 hour 30 minute papers, no calculator, what is on each, worked examples and June 2026 boundaries.