# 1. Introduction

Arrays are often used to store a list of numeric values. One common operation with arrays of numbers is computing their sum. In this guide, we'll design a TypeScript function that sums up all the numbers in an array.

# 2. Program Overview

We aim to create a function named sumArray that takes an array of numbers and returns their sum. The type annotations of TypeScript will ensure that our function accepts and works with only arrays of numbers.

# 3. Code Program

``````// Define a function to sum elements of an array
function sumArray(numbers: number[]): number {
let total = 0; // Initialize the total sum to 0
for (let num of numbers) {
total += num; // Add each number to the total sum
}
}

// Test the function
const numbers = [5, 2, 9, 1, 5, 6];
console.log(`The array is: [\${numbers}]`);
console.log(`The sum of the numbers is: \${sumArray(numbers)}`);
``````

### Output:

```The array is: [5, 2, 9, 1, 5, 6]
The sum of the numbers is: 28
```

# 4. Step By Step Explanation

1. We start by defining our sumArray function, which accepts an array called numbers.

2. Within this function, we establish a total variable and set its value to 0. This variable will serve to aggregate the sum of all numbers in the array.

3. Employing a for-of loop, we iterate over each number (num) within the numbers array.

4. For every iteration, the current number (num) is added to our total.

5. By the time the loop concludes, the total represents the aggregate sum of all numbers within the array.

6. The computed sum (total) is then returned.

7. To validate our function's accuracy, we evaluate it with a representative array of numbers and display both the array and its corresponding sum.