BSEB Inter Computer Science common mistakes
BSEB Inter Computer Science · Understand the traps and how to avoid them.
Calculates storage sizes by treating 1 KB as 1000 bytes and 1 MB as 1,000,000 bytes, then converts bit and byte values without dividing or multiplying by 8.
Decimal SI prefixes are used in everyday life, while computer memory is usually addressed in powers of 2; candidates also forget that 1 byte equals 8 bits.
What to do instead
Use 1 KB = 2^10 = 1024 bytes and 1 MB = 2^20 bytes unless the question explicitly states decimal units; write the bit-to-byte conversion as a separate step before calculating.
Converts a decimal fraction such as 0.375 to binary by writing the generated integer parts in the reverse order, producing 0.110 instead of 0.011.
Integer conversion uses remainders read bottom-to-top, and candidates wrongly apply the same reversal rule to the fractional part.
What to do instead
For fractional conversion, multiply the fraction by 2 repeatedly and record the integer part top-to-bottom as generated; stop when the fraction becomes zero or the required precision is reached, then verify by adding the binary place values.
Simplifies (A AND B)' as A' AND B' or (A OR B)' as A' OR B' when applying De Morgan's laws.
Candidates treat the negation of a compound Boolean expression like ordinary arithmetic distribution and forget that AND and OR swap.
What to do instead
Memorise and apply the two swaps: (A AND B)' = A' OR B', and (A OR B)' = A' AND B'. Check a small truth table when unsure.
States that ROM is volatile because it is memory, or says RAM permanently stores the BIOS and startup instructions.
The words RAM and ROM are both called memory, so candidates ignore the volatility and read/write differences that define primary storage.
What to do instead
Classify RAM as volatile read/write main memory used for running programs, and ROM as non-volatile firmware storage. Secondary storage such as a hard disk is non-volatile but is not main memory.
Saves a Notepad file as assignment.txt while Windows is hiding known file extensions, then submits assignment.txt.txt without noticing the double extension.
Notepad appends .txt automatically, and File Explorer hides the extension of known file types, so the displayed name looks correct even when the real name is wrong.
What to do instead
Turn on File name extensions in File Explorer's View settings, choose the correct Save as type, and verify the exact filename including its extension before submitting.
Writes if (x = 5) or while (n = 0) when the intention is to compare values, so the condition assigns a value instead of testing equality.
In C, the single equals sign is the assignment operator and its result is the assigned value; the code can compile without an error.
What to do instead
Use == for comparison. Compile with warnings enabled, and when a comparison is intended, place the constant on the left if helpful, for example if (5 == x), so an accidental assignment becomes a compile error.
Deletes the first node of a singly linked list with free(head); head = head->next; and then uses the new head or later traverses the list.
The code follows the visual left-to-right order and frees the node before saving the pointer stored inside it, leaving head pointing to freed memory.
What to do instead
Save the link first: struct node *next = head->next; free(head); head = next;. For middle-node deletion, keep a previous pointer and update prev->next before freeing the removed node.
Writes SELECT dept, COUNT(*) FROM emp WHERE COUNT(*) > 5 GROUP BY dept; and expects only departments with more than five employees.
WHERE filters individual rows before grouping, so aggregate functions such as COUNT cannot be used there; candidates confuse row filtering with group filtering.
What to do instead
Filter groups with HAVING after GROUP BY: SELECT dept, COUNT() FROM emp GROUP BY dept HAVING COUNT() > 5;. Use WHERE only for conditions on individual rows.
Says the MAC address changes when a laptop joins a different Wi-Fi network and that the IP address is a permanent hardware identifier.
Both are called addresses, so candidates mix the link-layer hardware address with the network-layer logical address assigned by DHCP or configuration.
What to do instead
Treat the MAC address as a 48-bit identifier burned into the network interface and used on the local link; treat the IP address as a logical address that can change with the network and is assigned by DHCP or manually.
Uses a p element as a general container, writing p Hello div World /div /p and expecting the div to sit inside the paragraph.
Browsers automatically close an open p element when a block-level element such as div starts, so the intended nesting is broken even though the source looks nested.
What to do instead
Use p only for paragraphs of phrasing content. Use div, section, or article as containers for block-level layout, and validate the nesting so the browser does not silently repair the structure.