Module assignment: the broken gradebook

The project

You have joined a small school as a volunteer developer. A teacher wrote a program called gradebook.js that reads a list of students with their scores and prints a report: each student's average and letter grade, the class average, and the top student. The teacher says: "It prints rubbish." Your job is to set up a proper workspace, reproduce the problem, find every bug using the method from the last lesson, fix them, and write down what you found.

This assignment uses the whole module: the folder and settings from lesson 1, the extensions and shortcuts from lesson 2, the terminal run and error reading from lesson 3, and the debugger from lesson 4. Plan for 60 to 90 minutes.

The spec

The program reads from standard input:

• The first line holds an integer n, the number of students.
• Then n lines follow. Each has a name (no spaces) and three scores, all separated by single spaces.

The program prints, in this order:

1. One line per student: NAME: AVERAGE (GRADE), with the average to one decimal place.
2. One line: class average: X, the mean of the students' averages, to one decimal place.
3. One line: top: NAME, the student with the highest average. If two students tie, the first one in the input wins.

Grades follow these bands, applied to the average: 90 or more is A, 75 or more is B, 60 or more is C, anything lower is F.

Example

Input:

4
Anisha 90 95 100
Ravi 70 80 75
Meera 55 60 65
Kabir 88 92 90

Expected output:

Anisha: 95.0 (A)
Ravi: 75.0 (B)
Meera: 60.0 (C)
Kabir: 90.0 (A)
class average: 80.0
top: Anisha

A second example, with a failing student:

2
Asha 40 50 30
Vik 59 59 59

Asha: 40.0 (F)
Vik: 59.0 (F)
class average: 49.5
top: Vik

The broken program

This is the teacher's code. It is a complete program: put the example input in the Input box below the code and press Run to see the rubbish for yourself.

With the first example as input, the output you see is:

Anisha: 3031700.0 (A)
Ravi: 236025.0 (A)
Meera: 185355.0 (A)
Kabir: 296430.0 (A)
class average: 1249836.7
top: 

Everything is wrong at once, which is typical: one bug can hide others behind it. There are four planted bugs, of four different kinds. You do not need to rewrite the program. Each fix changes one line or a few characters. Do not change the structure.

Requirements

Workspace

• Create a folder forgestack/module05/gradebook and open the forgestack folder (not a single file) in VS Code.
• Save the teacher's program as gradebook.js and the example input as week1-input.txt in that folder.
• Add a workspace settings file .vscode/settings.json with at least: editor.formatOnSave set to true, files.autoSave set to afterDelay, editor.tabSize set to 2.
• Add .vscode/extensions.json recommending esbenp.prettier-vscode.
• Add a .prettierrc that sets semi to true and tabWidth to 2, and format gradebook.js with it.

Running

• Run the program from the integrated terminal with the input piped from the file, using node gradebook.js < week1-input.txt, and record the wrong output in BUGS.md.
• Add a .vscode/tasks.json task named "run gradebook" that runs the current file, bound to Ctrl+Shift+B.
• Add a .vscode/launch.json configuration that debugs the current file in the integrated terminal.

Debugging

• Find all four bugs. For each, write an entry in BUGS.md with these four lines: Symptom (what you saw), Prediction (what it should have been), First wrong step (the line and what the value was), and Fix (the change).
• Use the debugger (a breakpoint and the Variables panel) to find at least one bug, and print statements to find at least one other. Note which tool you used for each.
• Use a conditional breakpoint or a logpoint at least once.
• After your fixes, the program prints the expected output for both examples above.
• Remove every debug print and breakpoint-related leftover.

Stretch

• Make the program accept an optional file path argument, so that node gradebook.js week1-input.txt also works, and use it in launch.json through the args setting.
• Write check.js (a short script that runs the program on three inputs and compares output) and make all three tests pass.
• Handle an input with a trailing blank line without crashing.

Grading rubric

Hints

Try each task before you open its hint. Hints are ordered from small nudge to bigger one.

The configuration files

If you get stuck on the workspace part, here are working versions. Try writing them yourself first.

.vscode/settings.json:

{
  "editor.formatOnSave": true,
  "editor.defaultFormatter": "esbenp.prettier-vscode",
  "files.autoSave": "afterDelay",
  "editor.tabSize": 2
}

.vscode/extensions.json:

{
  "recommendations": ["esbenp.prettier-vscode"]
}

.prettierrc:

{
  "semi": true,
  "tabWidth": 2
}

.vscode/tasks.json:

{
  "version": "2.0.0",
  "tasks": [
    {
      "label": "run gradebook",
      "type": "shell",
      "command": "node",
      "args": ["${file}"],
      "group": { "kind": "build", "isDefault": true }
    }
  ]
}

.vscode/launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "node",
      "request": "launch",
      "name": "Debug gradebook",
      "program": "${workspaceFolder}/module05/gradebook/gradebook.js",
      "args": ["${workspaceFolder}/module05/gradebook/week1-input.txt"],
      "console": "integratedTerminal"
    }
  ]
}

Notice that this launch.json passes the input file as an argument, so it only works after you complete the stretch item that reads process.argv[2]. If you skip the stretch, drop the args line and type the input into the terminal.

The check.js script

This is the self-checking script for the stretch goal. It runs gradebook.js on three inputs and compares the printed text with the expected text. Save it next to gradebook.js and run node check.js.

const { spawnSync } = require("child_process");
 
const cases = [
  {
    name: "sample class",
    input: "4\nAnisha 90 95 100\nRavi 70 80 75\nMeera 55 60 65\nKabir 88 92 90\n",
    expected: "Anisha: 95.0 (A)\nRavi: 75.0 (B)\nMeera: 60.0 (C)\nKabir: 90.0 (A)\nclass average: 80.0\ntop: Anisha\n",
  },
  {
    name: "single student",
    input: "1\nSolo 100 100 100\n",
    expected: "Solo: 100.0 (A)\nclass average: 100.0\ntop: Solo\n",
  },
  {
    name: "failing student",
    input: "2\nAsha 40 50 30\nVik 59 59 59\n",
    expected: "Asha: 40.0 (F)\nVik: 59.0 (F)\nclass average: 49.5\ntop: Vik\n",
  },
];
 
let passed = 0;
for (const c of cases) {
  const run = spawnSync("node", ["gradebook.js"], { input: c.input, encoding: "utf8" });
  if (run.stdout === c.expected) {
    console.log("PASS", c.name);
    passed++;
  } else {
    console.log("FAIL", c.name);
    console.log("  expected:", JSON.stringify(c.expected));
    console.log("  got:     ", JSON.stringify(run.stdout));
  }
}
console.log(passed + " of " + cases.length + " passed");

On the broken program it prints three FAIL lines. After your fixes it prints:

PASS sample class
PASS single student
PASS failing student
3 of 3 passed

Reference solution

Open this only after you have tried hard. First the four bugs, then the fixed code.

Anisha: 95.0 (A)
Ravi: 75.0 (B)
Meera: 60.0 (C)
Kabir: 90.0 (A)
class average: 80.0
top: Anisha

Asha: 40.0 (F)
Vik: 59.0 (F)
class average: 49.5
top: Vik

# Bugs in gradebook.js
 
## Bug 1: averages in the millions
Symptom: Anisha: 3031700.0 (A), every grade A.
Prediction: Anisha's average should be (90 + 95 + 100) / 3 = 95.0.
First wrong step: in average(), at sum = sum + s, s is the text "90", not a number.
Found with: debugger, breakpoint on that line, Variables panel showed s = "90" with quotes.
Fix: parts.slice(1).map(Number).
 
## Bug 2: wrong grades on exact boundaries
Symptom: Kabir (90.0) got B, Ravi (75.0) got C.
Prediction: 90 or more is A, 75 or more is B.
First wrong step: gradeFor uses > instead of >=.
Found with: print statement showing avg and the grade for each student.
Fix: >= in all three comparisons.
 
## Bug 3: empty top line
Symptom: "top: " with no name.
Prediction: topName should become Anisha on the first loop turn.
First wrong step: avg < topAvg is false for 95 < 0, so topName never changes.
Found with: conditional breakpoint on name === "Anisha".
Fix: avg > topAvg.
 
## Bug 4: class average 106.7
Symptom: class average 106.7 for the sample.
Prediction: (95 + 75 + 60 + 90) / 4 = 80.0.
First wrong step: the divisor is count - 1, which is 3.
Found with: Debug Console, evaluating classTotal and count.
Fix: divide by count.

Module summary

• VS Code opens a folder as the workspace, and the window has an activity bar, side bar, editor, panel and status bar.
• Settings come in default, user and workspace layers, and the .vscode folder shares project settings, tasks, debug setups and extension recommendations.
• Extensions are code, so you judge the publisher and install count first. Prettier formats and ESLint warns.
• The command palette, Ctrl+P, line-editing shortcuts, multiple cursors, F2 rename and snippets make editing fast.
• The integrated terminal runs node file.js from the current folder, and Node reads the file from disk, so you save first.
• Programs take input from stdin, arguments and environment variables, and report success with exit code 0.
• An error message has a place, a kind, a message and a stack trace, and you read it from the top.
• Debugging follows reproduce, predict, look, find, fix. The bug is at the first wrong step. Use prints, bisecting, breakpoints, stepping, watches and the call stack.