How IITM BS OPPE Marks Work: Public and Private Test Cases

IIT Madras does not publish how public and private test cases are scored in the OPPE. The student handbooks, the academics pages and the programme's rules say nothing about test cases or marks per test case. Only your course's OPPE instructions and grading document can tell you that. What the official rules do cover is the rest. Each course sets its own OPPE cut-off, missing it gives an I_OP grade, and the proctoring rules can cost you the exam. One practical point holds everywhere: passing the tests you can see does not mean you pass the ones you cannot.

What "public" and "private" test cases mean

These are student terms, not words from IITM's documents. On most coding platforms:

• Public test cases are the sample inputs and outputs you can see and run before you submit.
• Private test cases are hidden. The system runs them on your code after you submit and does not show you the inputs.

If your code only works for the examples shown, it can pass every public test and still fail private ones. Students often ask about exactly this after an OPPE. How IIT Madras converts passed tests into marks is not stated in any official source we found.

What the official rules say about OPPE marks

OPPE stands for Online Proctored Programming Exam. The DS academics page says some courses add programming exams to the usual assignments, quizzes and end term. A course with OPPE has two sittings, OPPE1 and OPPE2.

The handbooks write the pass line as "x out of 100", because each course sets its own. Here is how your OPPE result combines with the rest, in short:

If you miss the end term as well, other rows apply.

When you retake only the OPPE, both OPPEs are held for you and your assignment, quiz and end term marks carry over. In DS the fee is Rs 1,000 for a Foundation course and Rs 2,000 for a Diploma or degree course. The full table, including the ES fees, is in what OPPE is.

You also have to be "OPPE eligible". A rule from January 2026 says students retaking the OPPE after being marked ineligible had to submit the required assignments and the OPPE SCT to regain eligibility. Your grading document gives the normal rule.

Why code passes public tests but fails private ones

This is general programming advice, not an IITM rule.

1. Edge cases. Hidden tests often try an empty input, a single item, zero, negative numbers, repeated values or a tie. Test these yourself before you submit.
2. Output format. An extra space, a missing newline or text like "Answer:" can make a correct answer fail. Print exactly what the question shows.
3. Reading input. Code that assumes one line, or a fixed number of values, breaks when the hidden input is shaped differently.
4. Hard-coding. Printing the expected output of the sample cases only fools the public tests. Never try to trick the checker. The malpractice rules list exploiting a system weakness in exams as an offence. The penalty is a U grade in all courses of the term and a ban for the next two terms.

The habit that fixes most of this is writing your own small tests for every weekly programming assignment. Our Python OPPE practice guide has a routine and a table of common mistakes.

Proctoring rules that can cost you the exam

The programme's rules list suspicious behaviour during an OPPE. If you do any of these repeatedly after a warning, you can be removed from the exam link:

• looking away from the screen often, or at a phone;
• hands not on the desk at times;
• talking, or another person in the room;
• moving out of the camera's view, or a camera placed badly;
• not answering the proctor in the chat window.

A black or white screen seen by the proctor, or found in the post-exam audit, is treated as malpractice. You may be stopped from continuing or given zero for the subject. The rules tell you to make sure no black screen appears during the system compatibility test (SCT).

Common questions

Do I get partial marks if only some private test cases pass?

No official source we found says how partial passes are marked. Read your course's OPPE instructions, and ask on the course forum before the exam if they are unclear.

Is the OPPE cut-off the same in every course?

No. The handbooks write it as x out of 100 because each course sets its own. Your grading document for the term gives the number.

I passed all the public test cases but failed the OPPE. What now?

If your total score T is 40 or more, you get I_OP and retake only the OPPE next term. Your other marks carry over. See failed the OPPE for every case.

Can I see the private test cases after the exam?

The official sources do not say you can. Use the practice assignments with solutions to build habits, since those are the official practice material.