2023 Edexcel IGCSE Computer Science Practice Paper with Answers

An 8-bit register contains the binary pattern representing a signed integer in two's complement form: 10110100. The computer performs an arithmetic shift right by 2 places, followed by a logical bitwise OR with the binary mask 00001111. What is the resulting decimal value of this 8-bit register after these operations?

An organization uses asymmetric encryption to secure communication between a client and a server. The client wants to send a confidential message to the server, and also wants to ensure non-repudiation. Which combination of keys must be used to encrypt the message body for confidentiality, and to sign the message for non-repudiation?

A network administrator is configuring a Local Area Network (LAN) using a star topology. The administrator wants to minimize unnecessary network traffic and maximize security by directing data packets only to their intended destination devices. Which network hardware device should be used as the central node of the star topology, and what addressing scheme does it primarily use to route these data frames locally?

Consider the Boolean expression: \(Q = \overline{(A \cdot B)} + (B \cdot \overline{C})\). If the input values are \(A = 1\), \(B = 1\), and \(C = 0\), what is the evaluated output value of \(Q\), and which single logic gate represents the sub-expression \(\overline{(A \cdot B)}\)?

A student wants to compress high-fidelity audio recordings to play them on a portable device with limited storage. They can use either lossy MP3 compression or lossless FLAC compression. Which statement correctly describes the key differences and trade-offs between these two compression methods?

When multiple programs run simultaneously, the physical RAM can become fully occupied. To prevent the system from running out of memory, the operating system uses virtual memory. Which statement best describes how virtual memory functions in this situation?

An offline database contains a list of temperatures recorded at meteorological stations. A programmer is developing a Python subprogram `find_last_cold_day(temperatures, threshold)` that searches an array of numbers and returns the index of the last occurrence of a temperature that is strictly below the given `threshold`. If no such temperature is found, the subprogram must return `-1`.

For example:
`find_last_cold_day([12, 4, 8, 3, 15, 2], 5)` should return `5` (the index of the element `2`, which is the last value below `5`).

Which of the following Python implementations correctly and efficiently meets these requirements?

Consider the following pseudo-algorithm designed to perform a bubble sort on an array of integers `arr` containing `N` elements:

```text
SET outer TO 0
SET swapped TO True
WHILE outer < N - 1 AND swapped IS True
SET swapped TO False
FOR inner FROM 0 TO N - outer - 2
IF arr[inner] > arr[inner + 1] THEN
TEMP = arr[inner]
arr[inner] = arr[inner + 1]
arr[inner + 1] = TEMP
SET swapped TO True
ENDIF
ENDFOR
SET outer TO outer + 1
ENDWHILE
```

If the input array is `arr = [5, 1, 4, 2]`, complete a dry run to determine the state of the array after the FIRST full pass of the inner loop (when `outer` has completed its first iteration, i.e., `outer` is about to increment to `1`).

Choose the option that represents the state of `arr` and the value of `swapped` at this exact point.

A developer is implementing a function in Python that checks whether a given positive integer `num` is a prime number. They decide to use a helper variable `is_prime` as a boolean flag.

Here is the incomplete Python code:

```python
def check_prime(num):
if num <= 1:
return False

is_prime = True
#
for i in range(2, limit):
#
is_prime = False
break

return is_prime
```

To make this code run as efficiently as possible while still being mathematically correct, which of the following choices should replace `` and ``?

A student is creating a subprogram in Python to perform a Caesar cipher encryption on a string containing ONLY uppercase alphabetical characters (A-Z). The shift value `k` can be any positive integer (including values larger than 26).

The ASCII value of 'A' is 65, and 'Z' is 90.

Here is the incomplete Python code:

```python
def encrypt_caesar(plain_text, k):
cipher_text = ""
for char in plain_text:
# Convert character to a 0-25 scale
original_val = ord(char) - 65
# Apply shift and wrap around
#
# Convert back to character and append
cipher_text += chr(new_val + 65)
return cipher_text
```

Which of the following single-line code blocks should replace `` to correctly calculate `new_val`?

A program stores an image as a 2D list (grid) of dimensions N x N, representing pixel color values. The programmer wants to write a function `rotate_90_clockwise(grid)` that returns a new 2D list representing the image rotated 90 degrees clockwise.

Which of the following Python functions correctly implements this 90-degree clockwise rotation?

A developer is writing a robust Python function `count_even_integers_in_file(filename)` that opens a text file, reads numbers from it (where each number is stored on a separate line), and returns the count of even integers.

The function must:
1. Safely handle cases where the file does not exist by returning `-1`.
2. Ignore any lines that cannot be successfully cast to an integer (e.g., blank lines or text words) and continue processing the rest of the file.
3. Close the file properly regardless of any read/parse errors.

Which of the following implementations correctly satisfies all these requirements?