📚 Case Study Practice | 案例分析实战演练
In Year 10 CAIE Computer Science, case studies are used to bridge the gap between theoretical knowledge and real‑world problem‑solving. This article walks you through a complete practical example – designing a simple student grade management system – covering every stage from requirements analysis and algorithm design to testing and evaluation. By working through this case study, you will learn how to apply computational thinking, pseudocode, flowcharts, and testing strategies in an exam‑style context.
在 Year 10 CAIE 计算机科学中，案例分析用来弥合理论知识与实际问题解决之间的差距。本文将通过一个完整的实际示例——设计一个简易的学生成绩管理系统——逐步带你经历从需求分析、算法设计到测试与评估的每一个阶段。通过完成这个案例研究，你将学会如何在考试风格的情境中应用计算思维、伪代码、流程图以及测试策略。
1. Understanding the Case Study Scenario | 理解案例场景
The school administration requires a program to store and process student exam scores. The system should be able to input scores for a class of up to 30 students, calculate each student's average, determine the grade (A, B, C, D, F) based on the average, and display a summary of the number of students achieving each grade. Data must be stored in arrays and processed efficiently.
学校管理部门需要开发一个程序来存储和处理学生的考试成绩。该系统应能输入一个最多 30 名学生的班级的分数，计算每位学生的平均分，根据平均分评定等级（A、B、C、D、F），并显示获得各个等级的学生人数汇总。数据必须存储在数组中并高效处理。
The inputs are: student names and their scores in three subjects. The outputs are: each student's average and grade, plus a grade distribution table. The program must handle invalid input gracefully (e.g. scores outside 0–100).
输入内容为：学生姓名及其三门科目的成绩。输出内容为：每位学生的平均分和等级，外加一个等级分布表。程序必须妥善处理无效输入（例如分数超出 0–100 的范围）。
2. Decomposition and Requirements Analysis | 分解与需求分析
Breaking down the problem, we identify four core modules: data input, average calculation, grade assignment, and reporting. Each module can be developed and tested independently. We also need validation loops to ensure data integrity.
将问题分解后，我们识别出四个核心模块：数据输入、平均分计算、等级评定和报告生成。每个模块可以独立开发和测试。我们还需要验证循环来确保数据完整性。
The system requirements are:
- Accept up to 30 students (use a constant MAX_STUDENTS = 30)
- Store names in a 1D array and scores in a 2D array (30 × 3)
- Calculate average as a REAL number
- Assign grades using boundaries: A ≥ 80, B ≥ 70, C ≥ 60, D ≥ 50, F < 50
- Count grades and display a bar chart‑like summary using asterisks
系统需求如下：
- 最多接受 30 名学生（使用常量 MAX_STUDENTS = 30）
- 姓名存入一维数组，分数存入二维数组（30 × 3）
- 平均分计算为实数（REAL）
- 等级评定边界：A ≥ 80，B ≥ 70，C ≥ 60，D ≥ 50，F < 50
- 统计各等级人数并用星号显示类似条形图的摘要
3. Data Structures and Variables | 数据结构与变量
Choosing appropriate data structures is crucial. We will use:
DECLARE names : ARRAY[1:30] OF STRING
DECLARE scores : ARRAY[1:30, 1:3] OF INTEGER
DECLARE averages : ARRAY[1:30] OF REAL
DECLARE grades : ARRAY[1:30] OF CHAR
DECLARE countA, countB, countC, countD, countF : INTEGER
选择合适的数据结构至关重要。我们将使用：
DECLARE names : ARRAY[1:30] OF STRING
DECLARE scores : ARRAY[1:30, 1:3] OF INTEGER
DECLARE averages : ARRAY[1:30] OF REAL
DECLARE grades : ARRAY[1:30] OF CHAR
DECLARE countA, countB, countC, countD, countF : INTEGER
The 2D array scores[row, col] stores the three subject scores for each student. The averages array holds floating‑point results to avoid integer division errors. Grade counters are initialised to zero.
二维数组 scores[row, col] 存储每位学生的三门科目成绩。averages 数组存放浮点数结果以避免整除错误。等级计数器初始化为零。
4. Algorithm Design – Input and Validation | 算法设计——输入与验证
The input module uses a loop to enter data for exactly how many students the user wants (up to MAX). For each student, we read the name and then three scores. A validation loop ensures each score is between 0 and 100 inclusive. Pseudocode for one student's scores:
输入模块使用循环为用户指定的学生人数（最多 MAX）输入数据。对每位学生，我们读取姓名，然后输入三个成绩。验证循环确保每个成绩介于 0 到 100 之间（含）。一位学生成绩的伪代码如下：
FOR i ← 1 TO numStudents
INPUT names[i]
FOR j ← 1 TO 3
REPEAT
INPUT scores[i, j]
UNTIL scores[i, j] >= 0 AND scores[i, j] <= 100
NEXT j
NEXT i
The outer loop runs from 1 to the actual number of students entered by the user. The inner REPEAT…UNTIL structure traps invalid inputs and prompts the user again.
外层循环从 1 运行到用户实际输入的学生人数。内层的 REPEAT…UNTIL 结构捕捉无效输入并再次提示用户。
5. Algorithm Design – Calculating Averages | 算法设计——计算平均分
After all scores are stored, we iterate over each student, sum their three scores and divide by 3. To avoid integer division, we multiply one operand by 1.0 or explicitly store the result in a REAL variable. Pseudocode:
存储所有分数后，我们遍历每位学生，将其三科成绩相加并除以 3。为避免整除，我们可以将一个操作数乘以 1.0 或显式地将结果存入 REAL 变量。伪代码：
FOR i ← 1 TO numStudents
sum ← 0
FOR j ← 1 TO 3
sum ← sum + scores[i, j]
NEXT j
averages[i] ← sum / 3.0
NEXT i
This nested loop sums the columns for each row. Dividing by 3.0 ensures a REAL result is stored.
这个嵌套循环对每一行的各列求和。除以 3.0 可确保存储实数结果。
6. Algorithm Design – Grade Assignment | 算法设计——等级评定
Using the average, we determine a letter grade with a multi‑branch IF structure. The order of checks matters – we must test from highest boundary downward to avoid overlapping conditions.
利用平均分，我们通过多分支 IF 结构确定字母等级。检查的顺序很重要——我们必须从最高边界向下测试，避免条件重叠。
IF averages[i] >= 80 THEN
grades[i] ← 'A'
ELSE IF averages[i] >= 70 THEN
grades[i] ← 'B'
ELSE IF averages[i] >= 60 THEN
grades[i] ← 'C'
ELSE IF averages[i] >= 50 THEN
grades[i] ← 'D'
ELSE
grades[i] ← 'F'
ENDIF
Once the grade is known, we can also increment the corresponding counter variable (e.g. countA ← countA + 1). This builds the grade distribution while processing each student.
一旦确定等级，我们还可以增加相应的计数器变量（例如 countA ← countA + 1）。这样在处理每位学生时即可构建等级分布。
7. Output Design – Report and Visual Summary | 输出设计——报告与可视化摘要
The program must display a table showing each student's name, average (rounded to one decimal place), and grade. Afterwards, it prints the number of students achieving each grade and a simple horizontal bar chart using asterisks (*), where one asterisk represents one student.
程序必须显示一个表格，列出每位学生的姓名、平均分（保留一位小数）和等级。随后，打印获得每个等级的学生人数，并用星号（*）绘制简单的水平条形图，一个星号代表一名学生。
Example output:
Name Average Grade
Alice 88.7 A
Bob 62.3 C
...
Grade Distribution:
A: 5 *****
B: 8 ********
...
To print the asterisk bar, a loop repeats PRINT "*" for the count of each grade. Formatting ensures columns align.
要打印星号条柱，使用循环为每个等级的数量重复 PRINT "*"。格式化确保列对齐。
8. Flowchart Representation | 流程图表示
nts → Input loop (nested validation) → Calculate averages loop → Assign grades loop → Output table and histogram → Stop. The validation loop uses a decision diamond checking score < 0 OR score > 100; if true, loop back.
虽然完整的流程图太大无法在此完整展示，但关键结构元素如下所示。主流包括：开始 → 输入 numStudents → 输入循环（嵌套验证）→ 计算平均分循环 → 评定等级循环 → 输出表格和直方图 → 停止。验证循环使用判断菱形检查score < 0 OR score > 100；若为真则循环返回。
For CAIE exams, you must be able to interpret and draw flowchart symbols: rectangle for process, parallelogram for input/output, diamond for decision. Practice sketching the decision structure for the grade assignment.
在 CAIE 考试中，你必须能够解释和绘制流程图符号：矩形表示处理过程，平行四边形表示输入/输出，菱形表示判断。练习绘制等级评定的判断结构草图。
9. Testing Strategy | 测试策略
Testing is planned during design. We will use normal, boundary, and erroneous data. Test cases:
| Test Type | Inputs | Expected Outcome |
|---|---|---|
| Normal | Name: "Tom", Scores: 85, 90, 78 | Average=84.3, Grade=B |
| Boundary (upper) | 100, 100, 100 | Average=100, Grade=A |
| Boundary (lower) | 0, 0, 0 | Average=0, Grade=F |
| Boundary (grade edge) | 50, 50, 50 | Average=50, Grade=D |
| Erroneous | Score = -5, then 105 | Rejected; prompt until valid |
测试应在设计阶段规划。我们将使用正常、边界和错误数据。测试用例如上表。
We also test the grade counters by running a full class of 30 students with known averages and verifying the distribution output. A trace table for a small set of data (e.g. 3 students) helps confirm the logic.
我们还可以通过运行一个已知平均分的 30 名学生完整班级来测试等级计数器，并验证分布输出。对于少量数据（例如 3 名学生）的跟踪表有助于确认逻辑。
10. Trace Table Walkthrough | 跟踪表演练
To verify the algorithm, a trace table is constructed manually. Consider three students:
| i | j | score[i,j] | sum | averages[i] | grade |
|---|---|---|---|---|---|
| 1 | 1 | 80 | 80 | - | - |
| 1 | 2 | 90 | 170 | - | - |
| 1 | 3 | 70 | 240 | 80.0 | A |
Trace tables are extremely helpful in exams to demonstrate how variables change during execution. Always include a column for each variable and update them step‑by‑step.
跟踪表在考试中非常有用，可以展示变量在执行过程中如何变化。始终为每个变量包含一列，并逐步更新。
11. Evaluation and Refinements | 评估与改进
After implementation, evaluate the solution against the original requirements. Does it work for exactly 0 students? (Should handle gracefully.) Does it round averages correctly? (Our pseudocode simply stores a REAL; we could format output to 1 decimal place). Could we extend it to allow variable number of subjects? (Yes, by making the inner loop boundary dynamic.) The current design meets all core requirements but could be improved with a menu system to allow repeated runs.
实现后，对照原始需求评估解决方案。学生人数为 0 时能正常工作吗？（应妥善处理。）平均分四舍五入是否正确？（我们的伪代码仅存储 REAL 值；可以将输出格式化为一位小数。）能否扩展以允许可变数量的科目？（可以，通过使内层循环边界动态化。）当前设计满足所有核心需求，但可以通过添加菜单系统以允许重复运行来改进。
A key evaluation point is the use of parallel arrays versus a record structure. The CAIE syllabus expects familiarity with 1D and 2D arrays; using arrays is appropriate. However, an alternative design using user‑defined types might be more elegant but is not required at this level.
一个关键的评估点是使用并行数组与记录结构的对比。CAIE 教学大纲要求熟悉一维和二维数组；使用数组是合适的。然而，使用用户自定义类型的替代设计可能更优雅，但在此级别不作要求。
12. Summary and Exam Tips | 总结与考试技巧
This case study has illustrated a complete problem‑solving journey: understanding the problem, decomposing it, selecting data structures, designing algorithms with pseudocode and flowcharts, testing with trace tables and specific test data, and evaluating the solution. In your CAIE exam, you may be given an incomplete scenario and asked to complete parts of it. Always read the question carefully, identify inputs, processes, and outputs, and decide on the most suitable loop, condition, and array structure before writing code or pseudocode.
本案例分析展示了一个完整的问题解决历程：理解问题、分解问题、选择数据结构、使用伪代码和流程图设计算法、通过跟踪表和特定测试数据进行测试以及评估解决方案。在你的 CAIE 考试中，你可能会被给到一个不完整的场景，并要求你完成其中的部分内容。始终仔细阅读题目，识别输入、处理和输出，并在编写代码或伪代码之前确定最适合的循环、条件和数组结构。
Remember to practise drawing flowcharts for decision‑making and iterative processes. Neatly labelled trace tables can earn marks even if the final answer is slightly off. Finally, check boundary conditions (0, 100, grade boundaries) and always include validation.
请记住练习绘制决策和迭代过程的流程图。整齐标注的跟踪表即使最终答案略有偏差也能获得分数。最后，检查边界条件（0、100、等级边界），并始终包含验证。
Published by TutorHao | Computer Science Revision Series | aleveler.com
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