TypeScript Project: Student Manager

What you will build

A student manager keeps a roster in memory: each person has a name and a score. You print every row, then walk the same list once more to find the highest score and the student who earned it. The container is a typed array. The row type is an interface.

Names and scores are hardcoded so the program runs without readLine(). Open/typescript/try with Try it in TypeScript. That is the TypeScript editor.

A Student interface

An interface names the fields that belong together. name is a string.score is a number. One object is one student. The roster will hold several objects.

interface Student {
  name: string;
  score: number;
}

const a: Student = {
  name: "Ada",
  score: 91,
};

console.log(a.name + " " + a.score);

Output is Ada 91. The two values travel as one record instead of two parallel variables.

A typed array of students

The type is Student[]. push adds one student at the end. length is how many rows you have. A for...of loop visits each object in order.

interface Student {
  name: string;
  score: number;
}

const roster: Student[] = [];
roster.push({ name: "Ada", score: 91 });
roster.push({ name: "Lin", score: 84 });
roster.push({ name: "Omar", score: 97 });

console.log("Count: " + roster.length);
for (const s of roster) {
  console.log(s.name + " " + s.score);
}

Print a roster

A dedicated print function keeps the top of the file short. Pass the array so the function can read every field. Print a header first so the columns are obvious.

interface Student {
  name: string;
  score: number;
}

function printRoster(roster: Student[]): void {
  console.log("Name   Score");
  for (const s of roster) {
    console.log(s.name + "   " + s.score);
  }
}

const roster: Student[] = [];
roster.push({ name: "Ada", score: 91 });
roster.push({ name: "Lin", score: 84 });
roster.push({ name: "Omar", score: 97 });
printRoster(roster);

Complete program: top score

Start from the first student as the current best. Walk the rest of the array. When a score is higher, keep that student instead. If the roster is empty, print a message and skip the search. Ties keep the first name that reached that score.

interface Student {
  name: string;
  score: number;
}

function printRoster(roster: Student[]): void {
  console.log("Name   Score");
  for (const s of roster) {
    console.log(s.name + "   " + s.score);
  }
}

function printTop(roster: Student[]): void {
  if (roster.length === 0) {
    console.log("No students");
    return;
  }
  let top: Student = roster[0];
  for (let i = 1; i < roster.length; i++) {
    if (roster[i].score > top.score) {
      top = roster[i];
    }
  }
  console.log("Top: " + top.name + " with " + top.score);
}

const roster: Student[] = [];
roster.push({ name: "Ada", score: 91 });
roster.push({ name: "Lin", score: 84 });
roster.push({ name: "Omar", score: 97 });
roster.push({ name: "Nia", score: 88 });
printRoster(roster);
printTop(roster);

Omar has 97, the highest value in this demo. Change Lin to 99 and the top line should name Lin. The roster print stays in the same order you pushed.

Common mistakes

• Parallel arrays, one of names and one of scores. An interface keeps the pair aligned. If you delete a name from one list and forget the matching score, the rows no longer match.
• Using any[] for the roster. Then tsc will not catch a missing score field. AnnotateStudent[].
• Reading roster[0] when the array is empty. Check length === 0 first.
• Using >= in the top-score loop when you want the first winner of a tie. >keeps the earlier name.

Practice

1. Change Omar’s score from 97 to 90 and confirm Ada becomes the top student.
2. Add a fifth student with push and confirm the roster and the top-score line both update.
3. Print the lowest score as well, with the student name, and compute the class average as a number.

Next project: an Account class that refuses a withdrawal when the balance would go negative.