Arrays

Typed arrays store a sequence of values and keep element operations predictable.

typed array An annotation such as `number[]` says every element should be a number.

                            scores
                            scores = [82, 91, 76] (default)scores = [100, 95, 90]scores = [60, 70, 80]
                        

                            arrays.ts
                        
Replay: real traced execution (multi-file project)

                            const scores: number[] = [82, 91, 76];
scores.push(88);

let total: number = 0;
for (const score of scores) {
    total += score;
}

const average: number = total / scores.length;
console.log(`Scores: ${scores.join(", ")}`);
console.log(`Average: ${average}`);
const scores: number[] = [100, 95, 90];
scores.push(88);

let total: number = 0;
for (const score of scores) {
    total += score;
}

const average: number = total / scores.length;
console.log(`Scores: ${scores.join(", ")}`);
console.log(`Average: ${average}`);
const scores: number[] = [60, 70, 80];
scores.push(88);

let total: number = 0;
for (const score of scores) {
    total += score;
}

const average: number = total / scores.length;
console.log(`Scores: ${scores.join(", ")}`);
console.log(`Average: ${average}`);

                        
1scores ← 82,91,761const scores→ 82,91,76: number[] = [82, 91, 76];  //@scores=[100, 95, 90], [60, 70, 80]2scores.push(88);⋯
2//@scores=[100, 95, 90], [60, 70, 80]
scores ← 82,91,76,881const scores: number[] = [82, 91, 76];  //@scores=[100, 95, 90], [60, 70, 80]2scores.push(88);⋯values this step82,91,76 → 82,91,76,88//@scores=[100, 95, 90], [60, 70, 80]
scores
3total ← 01const scores: number[] = [82, 91, 76];  //@scores=[100, 95, 90], [60, 70, 80]2scores.push(88);34let total→ 0: number = 0;5for (const score of scores) {⋯
4total ← 82⋯4let total: number = 0;5for (const score of scores) {6    total += score82;7}⋯values this step82total
5total ← 173⋯4let total: number = 0;5for (const score of scores) {6    total += score91;7}⋯values this step173total
6total ← 249⋯4let total: number = 0;5for (const score of scores) {6    total += score76;7}⋯values this step249total
7total ← 337⋯4let total: number = 0;5for (const score of scores) {6    total += score88;7}⋯values this step337total
8average ← 84.25, total ← 337⋯6    total += score;7}89const average→ 84.25: number = total→ 337 / scores.length4;10console.log(`Scores: ${scores.join(", ")}`);⋯
9console.log(`Scores: ${scores.join(", ")}`);⋯9const average: number = total / scores.length;10console.log(`Scores: ${scores82,91,76,88.join(", ")}`);11console.log(`Average: ${average}`);⋯outputScores: 82, 91, 76, 88
10console.log(`Average: ${average}`);⋯9const average: number = total / scores.length;10console.log(`Scores: ${scores.join(", ")}`);11console.log(`Average: ${average84.25}`);⋯outputAverage: 84.25
1scores ← 100,95,901const scores→ 100,95,90: number[] = [100, 95, 90];2scores.push(88);⋯
2scores ← 100,95,90,881const scores: number[] = [100, 95, 90];2scores.push(88);⋯values this step100,95,90 → 100,95,90,88scores
3total ← 01const scores: number[] = [100, 95, 90];2scores.push(88);34let total→ 0: number = 0;5for (const score of scores) {⋯
4total ← 100⋯4let total: number = 0;5for (const score of scores) {6    total += score100;7}⋯values this step100total
5total ← 195⋯4let total: number = 0;5for (const score of scores) {6    total += score95;7}⋯values this step195total
6total ← 285⋯4let total: number = 0;5for (const score of scores) {6    total += score90;7}⋯values this step285total
7total ← 373⋯4let total: number = 0;5for (const score of scores) {6    total += score88;7}⋯values this step373total
8average ← 93.25, total ← 373⋯6    total += score;7}89const average→ 93.25: number = total→ 373 / scores.length4;10console.log(`Scores: ${scores.join(", ")}`);⋯
9console.log(`Scores: ${scores.join(", ")}`);⋯9const average: number = total / scores.length;10console.log(`Scores: ${scores100,95,90,88.join(", ")}`);11console.log(`Average: ${average}`);⋯outputScores: 100, 95, 90, 88
10console.log(`Average: ${average}`);⋯9const average: number = total / scores.length;10console.log(`Scores: ${scores.join(", ")}`);11console.log(`Average: ${average93.25}`);⋯outputAverage: 93.25
1scores ← 60,70,801const scores→ 60,70,80: number[] = [60, 70, 80];2scores.push(88);⋯
2scores ← 60,70,80,881const scores: number[] = [60, 70, 80];2scores.push(88);⋯values this step60,70,80 → 60,70,80,88scores
3total ← 01const scores: number[] = [60, 70, 80];2scores.push(88);34let total→ 0: number = 0;5for (const score of scores) {⋯
4total ← 60⋯4let total: number = 0;5for (const score of scores) {6    total += score60;7}⋯values this step60total
5total ← 130⋯4let total: number = 0;5for (const score of scores) {6    total += score70;7}⋯values this step130total
6total ← 210⋯4let total: number = 0;5for (const score of scores) {6    total += score80;7}⋯values this step210total
7total ← 298⋯4let total: number = 0;5for (const score of scores) {6    total += score88;7}⋯values this step298total
8average ← 74.5, total ← 298⋯6    total += score;7}89const average→ 74.5: number = total→ 298 / scores.length4;10console.log(`Scores: ${scores.join(", ")}`);⋯
9console.log(`Scores: ${scores.join(", ")}`);⋯9const average: number = total / scores.length;10console.log(`Scores: ${scores60,70,80,88.join(", ")}`);11console.log(`Average: ${average}`);⋯outputScores: 60, 70, 80, 88
10console.log(`Average: ${average}`);⋯9const average: number = total / scores.length;10console.log(`Scores: ${scores.join(", ")}`);11console.log(`Average: ${average74.5}`);⋯outputAverage: 74.5

Follow the Scores

scores starts as [82, 91, 76].
scores.push(88) adds 88 at the end.
The loop adds all four scores into total.
total is 337.
average is 337 / 4, so the program prints Average: 84.25. | step | value | | --- | --- | | starting scores | 82, 91, 76 | | after push | 82, 91, 76, 88 | | total | 337 | | average | 84.25 | | starting scores | after push | total | average | | --- | --- | --- | --- | | 100, 95, 90 | 100, 95, 90, 88 | 373 | 93.25 | | 82, 91, 76 | 82, 91, 76, 88 | 337 | 84.25 | | 60, 70, 80 | 60, 70, 80, 88 | 298 | 74.5 |

Exercise: arrays.ts

Reproduce the default scores and average, then try one listed starting score set and predict the total and average.