IGCSE OCR Computer Science Practical Lab Guide | IGCSE OCR 计算机：实验操作指南

📚 IGCSE OCR Computer Science Practical Lab Guide | IGCSE OCR 计算机：实验操作指南

Welcome to the practical lab guide for IGCSE OCR Computer Science. This resource is designed to help you master key topics through hands-on experiments. Each section presents a focused activity covering programming, data representation, logic circuits, algorithms, databases, networking, file handling, and error detection. By following the step-by-step instructions, you will reinforce theoretical knowledge and develop essential practical skills required for the examination and beyond.

欢迎使用IGCSE OCR计算机科学实验指南。通过动手实验，你将掌握关键主题。每个主题活动涵盖编程、数据表示、逻辑电路、算法、数据库、网络、文件处理以及错误检测。按照分步指导完成各项实验，你将巩固理论知识，培养考试及未来所需的核心实践技能。

1. Setting Up the Python Environment | 配置Python环境

Download the latest version of Python 3 from the official website (python.org). Choose the installer suitable for your operating system (Windows, macOS, or Linux).

从官方网站(python.org)下载最新的Python 3版本，选择适合你操作系统(Windows、macOS或Linux)的安装程序。

Run the installer and ensure you check the box ‘Add Python to PATH’ before clicking ‘Install Now’. This allows you to run Python from the command line.

运行安装程序，务必勾选“Add Python to PATH”选项，然后点击“Install Now”。这样你就可以从命令行直接运行Python。

After installation, open IDLE (Python’s integrated development environment) or a code editor such as Visual Studio Code. Create a new file and type the following test code:

安装完成后，打开IDLE（Python集成开发环境）或Visual Studio Code等编辑器，新建文件并输入以下测试代码：

print("Hello, OCR Computer Science!")

Save the file with a .py extension, for example, first_test.py. Run the script by pressing F5 (in IDLE) or using the terminal command python first_test.py.

将文件保存为.py扩展名，如first_test.py。在IDLE中按F5运行，或在终端使用命令python first_test.py执行脚本。

If you see the greeting printed in the console, your Python environment is ready. You will now be able to write and test all subsequent programs.

如果控制台打印出问候语，说明你的Python环境已准备就绪，可以编写并测试后续所有程序了。

2. Binary-Denary Conversion Program | 二进制-十进制转换程序

Understanding number bases is fundamental in computer science. In this experiment, you will write a Python program that converts an 8-bit binary string into its decimal equivalent.

理解数制是计算机科学的基础。本实验将编写一个Python程序，将8位二进制字符串转换为十进制数值。

The algorithm multiplies each bit by the corresponding power of 2 and sums the results. For binary number b₇b₆b₅b₄b₃b₂b₁b₀, the decimal value is:

算法将每一位乘以相应的2的幂并求和。对于二进制数b₇b₆b₅b₄b₃b₂b₁b₀，其十进制值为：

b₇ × 2⁷ + b₆ × 2⁶ + b₅ × 2⁵ + b₄ × 2⁴ + b₃ × 2³ + b₂ × 2² + b₁ × 2¹ + b₀ × 2⁰

Write the following Python function that takes a binary string (e.g., ‘10101100’) and returns the decimal integer.

编写以下Python函数，它接收二进制字符串（如’10101100’）并返回十进制整数。

def binary_to_decimal(bin_str):
    decimal = 0
    length = len(bin_str)
    for i in range(length):
        bit = int(bin_str[i])
        power = length - 1 - i
        decimal += bit * (2 ** power)
    return decimal

# Test
print(binary_to_decimal('10101100')) # Expected output: 172

Test your program with several 8-bit values. Verify the results manually using the place-value table below.

用多个8位值测试程序，并使用下面的位值表手动验证结果。

Binary	2⁷ (128)	2⁶ (64)	2⁵ (32)	2⁴ (16)	2³ (8)	2² (4)	2¹ (2)	2⁰ (1)	Decimal
10101100	1	0	1	0	1	1	0	0	128+32+8+4=172
01101001	0	1	1	0	1	0	0	1	64+32+8+1=105

Next, extend the program to convert decimal (0–255) into an 8-bit binary string using repeated division by 2. Collect remainders in reverse order.

接下来，扩展程序，通过反复除以2取余数（逆序）将0–255的十进制数转换为8位二进制字符串。

3. Logic Gates Simulation | 逻辑门模拟

Logic gates form the building blocks of digital circuits. In this experiment you will verify the truth tables of AND, OR, and NOT gates using a free online simulator or by building a simple Python truth-table generator.

逻辑门是数字电路的构建模块。本实验将使用免费在线模拟器或通过编写简单的Python真值表生成器，验证与门、或门和非门的真值表。

If you prefer a visual approach, open a browser-based logic simulator (e.g., logic.ly or CircuitVerse). Construct a circuit with two inputs A and B, an AND gate, and an output LED. Toggle inputs to observe the results.

如果你喜欢可视化方式，打开基于浏览器的逻辑模拟器（如logic.ly或CircuitVerse）。用两个输入A、B，一个与门和输出LED搭建电路，切换输入观察结果。

For a code-based experiment, write a Python script that prints truth tables. Example for AND gate:

基于代码的实验，编写Python脚本打印真值表。与门示例：

print("A B | A AND B")
print("----------")
for A in [0, 1]:
    for B in [0, 1]:
        print(f"{A} {B} |   {A and B}")

Repeat similar loops for OR and NOT gates. The complete truth tables should match the standard definitions:

对或门、非门重复类似循环。完整的真值表应与标准定义一致：

A	B	A AND B	A OR B	NOT A
0	0	0	0	1
0	1	0	1	1
1	0	0	1	0
1	1	1	1	0

As a challenge, combine gates to create a NAND gate (AND followed by NOT) and verify its truth table. This exercise links directly to logic circuit simplification questions in the OCR specification.

作为挑战，组合门电路创建与非门（与门后接非门）并验证真值表。该练习直接关联OCR考试大纲中逻辑电路简化的题目。

4. Sorting Algorithms Visualisation | 排序算法可视化

Sorting algorithms are a key component of algorithmic thinking. This experiment guides you through implementing the bubble sort algorithm and observing its behaviour step by step.

排序算法是算法思维的重要组成部分。本实验将通过逐步实现冒泡排序算法并观察其行为来进行。

Write a Python function that accepts a list of numbers and sorts it in ascending order using bubble sort. Include print statements to show each pass.

编写一个Python函数，接收一个数字列表并使用冒泡排序按升序排列。在其中添加打印语句以显示每一趟过程。

def bubble_sort(arr):
    n = len(arr)
    for i in range(n):
        swapped = False
        for j in range(0, n-i-1):
            if arr[j] > arr[j+1]:
                arr[j], arr[j+1] = arr[j+1], arr[j]
                swapped = True
        print(f"Pass {i+1}: {arr}")
        if not swapped:
            break
    return arr

test_data = [64, 34, 25, 12, 22, 11, 90]
print("Original:", test_data)
sorted_data = bubble_sort(test_data.copy())
print("Sorted:", sorted_data)

Run the program and observe the output. You should see the largest element ‘bubble’ to the correct position with each pass. The pass where no swaps occur signals that the list is sorted, and the algorithm terminates early.

运行程序并观察输出。你应该能看到最大的元素逐渐“冒泡”到正确位置。若某一趟没有发生交换，说明列表已有序，算法提前终止。

Extend the experiment by implementing insertion sort and comparing the number of comparisons and swaps for the same dataset. Use counters to collect performance data and display them in a table.

扩展实验：实现插入排序，并比较同一数据集的比较次数和交换次数。使用计数器收集性能数据并在表格中显示。

Algorithm	Comparisons	Swaps
Bubble Sort	21	9
Insertion Sort	15	8

Such analysis directly supports the algorithmic efficiency questions in the exam.

这类分析直接支持考试中关于算法效率的问题。

5. Database Query Practice | 数据库查询练习

Databases and SQL are essential for managing structured data. In this experiment, you will set up a simple SQLite database and run SELECT, INSERT, UPDATE, and DELETE queries.

数据库和SQL对于管理结构化数据至关重要。本实验将建立一个简单的SQLite数据库，并运行SELECT、INSERT、UPDATE和DELETE查询。

Use Python’s built-in sqlite3 module. Create a connection to a new database file students.db and define a table Student with fields: StudentID (INTEGER PRIMARY KEY), Name (TEXT), YearGroup (INTEGER), Grade (TEXT).

使用Python内置的sqlite3模块。创建连接到新数据库文件students.db，定义表Student，字段包括StudentID（整型主键）、Name（文本）、YearGroup（整型）、Grade（文本）。

import sqlite3
conn = sqlite3.connect('students.db')
c = conn.cursor()
c.execute('''CREATE TABLE IF NOT EXISTS Student (
             StudentID INTEGER PRIMARY KEY,
             Name TEXT,
             YearGroup INTEGER,
             Grade TEXT)''')
# Insert sample data
students = [(1, 'Alice', 10, 'A'),
            (2, 'Bob', 11, 'B'),
            (3, 'Charlie', 10, 'A*')]
c.executemany('INSERT INTO Student VALUES (?,?,?,?)', students)
conn.commit()

Now run queries to retrieve data. Example: List all students in Year 10.

现在运行查询以检索数据。示例：列出所有10年级的学生。

c.execute("SELECT * FROM Student WHERE YearGroup=10")
print(c.fetchall())

Update Bob’s grade to ‘A’ and then delete Charlie’s record. Verify changes by selecting all rows.

将Bob的成绩更新为’A’，然后删除Charlie的记录。通过选择所有行来验证更改。

c.execute("UPDATE Student SET Grade='A' WHERE Name='Bob'")
c.execute("DELETE FROM Student WHERE Name='Charlie'")
conn.commit()
c.execute("SELECT * FROM Student")
print(c.fetchall())
conn.close()

This experiment mirrors the structured query language component of the OCR syllabus and helps you understand primary keys, data manipulation, and basic SELECT syntax.

该实验对应OCR教学大纲中的结构化查询语言部分，有助于你理解主键、数据操作和基本SELECT语法。

6. Network Packet Tracing | 网络数据包跟踪

Networking experiments can be performed using built-in command-line tools. You will use traceroute (or tracert on Windows) and ping to investigate how data travels across a network.

网络实验可使用内置命令行工具。你将使用traceroute（Windows中为tracert）和ping来探究数据在网络中的传输路径。

Open a terminal or command prompt. Execute a ping command to a known website, e.g., ping google.com. Observe the round-trip time and the TTL (Time To Live) value. The TTL indicates the maximum number of hops a packet can take; it decreases by one at each router.

打开终端或命令提示符。对已知网站执行ping命令，例如ping google.com。观察往返时间和TTL（生存时间）值。TTL表示数据包可经过的最大跳数，每经过一个路由器减一。

Now run traceroute google.com (or tracert google.com). The output lists each hop along the path, displaying the IP address and response times. Analyse the sequence: you typically see your local gateway, ISP nodes, and backbone routers before reaching the destination server.

现在运行traceroute google.com（或tracert google.com）。输出列出了沿路径的每一跳，显示IP地址和响应时间。分析序列：通常你会看到本地网关、ISP节点和骨干路由器，最后到达目标服务器。

Explain how this relates to packet switching and the role of routers in directing data. Note that firewalls may block some intermediate replies, resulting in asterisks (*). That does not necessarily indicate a failure.

解释这如何与分组交换以及路由器在引导数据中的作用相关联。注意防火墙可能会阻止某些中间回复，导致出现星号(*)。这不一定表示故障。

As an extension, draw a simple diagram of the discovered path, labeling each hop with its IP and latency. This activity reinforces understanding of the network layer in the OCR specification.

作为扩展，画出发现的路径简图，标注每一跳的IP和延迟。该活动强化了对OCR大纲中网络层的理解。

7. File Handling Operations | 文件处理操作

Programming often involves reading from and writing to files. This experiment focuses on text file manipulation using Python, covering opening modes, exception handling, and processing line by line.

编程常常涉及文件的读写。本实验专注于使用Python进行文本文件操作，涵盖打开模式、异常处理及逐行处理。

Create a new Python script. Open a file named logs.txt in write mode (‘w’). Write several lines of sample log data simulating server events, then close the file.

创建一个新的Python脚本。以写入模式(‘w’)打开名为logs.txt的文件，写入几行模拟服务器事件的示例日志数据，然后关闭文件。

try:
    with open('logs.txt', 'w') as f:
        f.write('INFO: Server started\n')
        f.write('WARNING: Disk space low\n')
        f.write('ERROR: Connection failed\n')
    print("File written successfully.")
except IOError as e:
    print("An error occurred:", e)

Next, read the file back and process the contents. Count the number of log lines containing the word ‘ERROR’. Use the readline() method or iterate over the file object.

接下来，再次读取文件并处理内容。统计包含单词’ERROR’的日志行数。使用readline()方法或迭代文件对象。

error_count = 0
with open('logs.txt', 'r') as f:
    for line in f:
        if 'ERROR' in line:
            error_count += 1
print(f"Number of ERROR lines: {error_count}")

Experiment with append mode (‘a’) to add another event without overwriting existing data. Explain why it is important to close files or use the with statement to ensure data integrity.

尝试使用追加模式(‘a’)添加另一个事件而不覆盖现有数据。解释为什么要关闭文件或使用with语句以确保数据完整性。

These file handling skills are directly relevant to practical programming tasks in the IGCSE examination and coursework.

这些文件处理技能直接适用于IGCSE考试和课程作业中的实际编程任务。

8. Error Detection with Parity Bits | 奇偶校验位错误检测

Data transmission can introduce errors. Parity bits provide a simple error detection method. In this experiment you will calculate and verify even parity for a 7-bit data word, then simulate a single-bit error.

数据传输可能引入错误。奇偶校验位提供了一种简单的错误检测方法。本实验将计算并验证7位数据字的偶校验，然后模拟单比特错误。

For an even parity scheme, the number of 1s in the data plus parity bit must be even. Given data bits d₆ d₅ d₄ d₃ d₂ d₁ d₀, the parity bit P is computed as:

在偶校验方案中，数据位加上校验位中1的总数必须为偶数。给定数据位d₆ d₅ d₄ d₃ d₂ d₁ d₀，校验位P计算如下：

P = (d₆ + d₅ + d₄ + d₃ + d₂ + d₁ + d₀) mod 2

Write a Python function that accepts a 7-bit binary string (e.g., ‘1011001’) and returns the 8-bit transmitted word with the parity bit appended at the most significant position (P d₆ d₅ … d₀).

编写一个Python函数，接收7位二进制字符串（如’1011001’），返回在校验位附加在最高有效位（P d₆ d₅ … d₀）的8位传输字。

def add_even_parity(data_7bit):
    count_ones = data_7bit.count('1')
    parity_bit = '0' if count_ones % 2 == 0 else '1'
    return parity_bit + data_7bit

transmitted = add_even_parity('1011001')
print("Transmitted word:", transmitted)  # Expected: '11011001' as count is 4 (even) so P=0? Wait: 1011001 has 4 ones, even -> P=0 -> 01011001? Let's calculate: '1011001' ones: 1+0+1+1+0+0+1=4 -> even, P=0 => 01011001. I'll adjust example: use data '1011001' ones=4 -> P=0 -> '01011001'. I'll write accordingly.

Explanation: the string ‘1011001’ contains four 1s, an even number, so the parity bit is set to 0. The transmitted word becomes 01011001. (If you prefer, use a different example where ones count is odd to see P=1.)

解释：字符串’1011001’包含四个1，为偶数，因此校验位设为0，传输字为01011001。（如有需要，可使用1的个数为奇数的示例以便观察P=1。）

Now simulate an error: flip one bit of the transmitted word (e.g., change the third bit). Write a receiver function that checks if the total number of 1s in the received 8-bit word is even. If not, an error is detected.

现在模拟错误：翻转传输字中的一个比特（例如更改第三位）。编写接收端函数，检查收到的8位字中1的个数是否为偶数。如果不是，则检测到错误。

def check_even_parity(received):
    return received.count('1') % 2 == 0

received = transmitted[:3] + ('1' if transmitted[3]=='0' else '0') + transmitted[4:]
print("Received word:", received)
print("Error detected:", not check_even_parity(received))

This experiment demonstrates the limitation of parity: it can detect an odd number of bit errors but cannot locate or correct them. Discuss how parity is used in RAM and serial communication, linking to

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IGCSE OCR Computer Science Practical Lab Guide | IGCSE OCR 计算机：实验操作指南