Parsing and Multiplying Numbers in TypeScript

Welcome! In this unit, we have an exciting and practical task that will test your TypeScript programming skills. We will be parsing strings and making type conversions. So, let's dive into it!

Our task for the day involves creating a TypeScript function called parseAndMultiplyNumbers(). This function is designed to accept a string as input. However, it's not just any string — the input we'll consider is a playful mix of numbers and words.

The purpose of this function is to analyze the input string, extract all the numbers, convert these numbers (currently string types) into integer data types, and then multiply all these numbers together. The final output? It's the product of all those numbers!

Here's an illustration for clarification. Given the input string "I have 2 apples and 5 oranges," our function should return the product of 2 and 5, which is 10.

The primary task is to parse the string and identify the numbers. To do that, let's create an empty string num to accumulate digits and an array numbers to collect all the numbers we find:

let inputString: string = "I have 2 apples and 5 oranges";
let num: string = "";
let numbers: number[] = [];

The next step requires iterating through the input string character by character. When we encounter a digit, we append it to our num string. If a character isn’t a digit and num isn’t empty, it means we've reached the end of a number.

At this point, we convert num to an integer, add it to the numbers array, and reset num to an empty string. If the character isn’t a digit and num is empty, we simply skip and progress.

To check if a character is a digit, we use the isNaN() function. The isNaN() function returns true if a value is NaN (not a number) and false otherwise. However, since we want to know if a character is a digit, we use the negation !isNaN(ch as any). This will return false for non-digit characters and true for digits. Additionally, we check that the character isn't a space (ch !== ' ') to avoid spaces being counted as numbers.

for (let ch of inputString) {
    if (!isNaN(ch as any) && ch !== ' ') { // Check if character is a digit
        num += ch;
    } else if (num !== "") {
        numbers.push(parseInt(num)); // Convert num to integer and add it to numbers array
        num = "";
    }
}
// After the loop, we must check if 'num' is not empty
// because it indicates that the last part of the string contains a number.
if (num !== "") {
    numbers.push(parseInt(num));
}
console.log(numbers); // Output should be [2, 5]