Nepal SEE Computer Science common mistakes
Nepal SEE Computer Science · Understand the traps and how to avoid them.
Writing the QBasic program for a number problem (prime, palindrome, Armstrong) without declaring and initialising the loop/accumulator variables, so the program either fails to compile or prints wrong output.
Candidates memorise the logic of the algorithm but skip the practical setup - DIM statements, initial values like s = 0 or f = 1, and the INPUT line - because they practise by reading programs rather than typing and running them.
What to do instead
Adopt a fixed skeleton for every program: CLS, variable declarations/initialisations, INPUT, processing loop, PRINT, END. Run each program at least once in QBasic with a test value (e.g. 29 for prime, 121 for palindrome) and fix errors before the exam.
Confusing the two QBasic loop forms - using WEND to close a FOR...NEXT loop or NEXT to close a WHILE loop - and mixing DO...LOOP WHILE with DO WHILE...LOOP syntax.
The four loop constructs look similar on paper, and candidates revise them by reading rather than writing, so the matching keyword pairs blur together.
What to do instead
Make a one-page table pairing each opening statement with its mandatory closing statement (FOR/NEXT, WHILE/WEND, DO WHILE...LOOP, DO...LOOP WHILE) and write one short working program per form, checking each runs without a syntax error.
Mixing up the number systems when converting - for example writing the binary of 25 as 11001 but then converting 11001 back as decimal 25 in base 8, or forgetting that hexadecimal uses A–F for 10–15.
Candidates learn the conversion steps as separate tricks (divide by 2, group in fours) without a single consistent method, so errors appear when the direction changes or when a remainder exceeds 9.
What to do instead
Use one method for all directions: decimal to any base by repeated division collecting remainders bottom-up, any base to decimal by positional expansion. Practise 10 mixed conversions, including one hexadecimal answer containing a letter, and verify by converting back.
Describing a logic gate or Boolean expression from memory of its name rather than its truth table - e.g. claiming a NAND gate outputs 1 only when both inputs are 1, or simplifying A + A·B to A·B.
Gate symbols and Boolean laws are learned visually and verbally, and candidates rarely draw truth tables during revision, so the actual output pattern is never checked.
What to do instead
For every gate question, draw the full truth table first (all input combinations) and read the answer off it. Memorise the three or four Boolean identities actually used (A + A·B = A, A·A' = 0, A + A' = 1) and prove each with a two-row table.
Answering number-system and memory-unit questions with the wrong unit scale - treating 1 KB as 1000 bytes, 1 MB as 1000 KB, or confusing bit with byte when computing storage or transmission size.
Everyday decimal usage (kilo = 1000) conflicts with the binary convention used in computer science, and the bit/byte distinction is glossed over in quick reading.
What to do instead
Memorise the ladder 8 bits = 1 byte, 1024 B = 1 KB, 1024 KB = 1 MB, 1024 MB = 1 GB, 1024 GB = 1 TB, and always write the unit next to every number in a calculation. Do three storage-size conversions and one bit-versus-byte comparison.
Writing SQL queries with the clauses in the wrong order or misspelling keywords - e.g. SELECT ... WHERE ... FROM, using = instead of LIKE for a pattern match, or omitting quotes around text values.
Candidates remember the individual keywords but not the fixed clause sequence, and practice is often done by copying queries rather than composing them from a stated requirement.
What to do instead
Memorise the order SELECT–FROM–WHERE–GROUP BY–HAVING–ORDER BY. For each practice question, write the query from scratch, then check three things: clause order, quotes around text, and the correct operator (LIKE with % for patterns, = for exact match).
Confusing the roles of primary key, foreign key, and candidate key in a table-design question, or declaring a column as primary key that can hold duplicate or null values.
The definitions overlap in wording, and candidates match on the word 'key' rather than on the uniqueness and null rules that actually distinguish the three.
What to do instead
Use a one-line test for each: primary key = unique and never null, one per table; candidate key = any column that could serve as primary key; foreign key = a column matching another table's primary key. Apply the test to the specific columns named in the question before answering.
Describing the OSI model or TCP/IP layers with the wrong layer for a device or protocol - e.g. placing a router at the data link layer, a switch at the network layer, or HTTP at the transport layer.
Layer names and device functions are memorised as separate lists, and candidates never build a single mapping from layer to device to protocol.
What to do instead
Build one table with seven rows: layer number, layer name, one device, one protocol, one data unit. Recite it top-down and bottom-up, then answer device/protocol questions by locating the row in that table rather than guessing.
Giving vague, one-clause definitions for cyber-safety and computer ethics terms (phishing, hacking, virus, copyright, digital footprint) that do not state how the term differs from its neighbours.
These are treated as easy marks and revised by skimming a list, so the answer names the concept without the distinguishing feature the marker is looking for.
What to do instead
For each term, prepare a two-part definition: what it is plus how it differs from the closest similar term (phishing vs hacking, virus vs worm). Write each in one full sentence and check it contains both parts before moving on.
Losing marks on the long-answer question by listing bullet points where the question says 'explain' or 'describe', or by describing a number-system/computer-architecture process without a worked example.
Candidates manage time by writing short answers everywhere, and they do not check the command word (define, explain, describe, compare) against the mark allocation.
What to do instead
Before writing, underline the command word and note the marks. For 'explain' or 'describe', write connected sentences with a reason or a worked example for each mark; for 'compare', use two named features. Reserve the last ten minutes to check that each long answer matches its command word.