# Vowels Count Algorithm

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Welcome! Today I’ll show you a commonly asked algorithm in tech interviews: the vowel counter.  
As you can see if you’ve been following my series, the most frequently asked algorithms are related with [Arrays](https://medium.com/@rubenosmaralvarado/we-need-to-talk-about-arrays-89ecfb402979), that’s why we started with that data structrue in the first post. Well, this problem will be solved using it too.  
So, let’s start!

#### Problem Statement

> *Given a string, count the number of vowels it contains. Vowels are the characters ‘a’, ‘e’, ‘i’, ‘o’, and ‘u’.*

Easy, right? While straightforward, this problem is excellent for learning fundamental concepts like loops and string manipulation.

The problem statement clearly defines both the input (a string) and the output (a number). It also hints at the solution by listing the specific characters we need to count. Let me demonstrate this better with code.

#### Algorithm to solve it

* Declare a `count` variable to register each appearance of a vowels in the input.
    

```typescript
let count = 0;
```

* Next, create an array with the expected chars to be found, do you remember that I mentioned in the problem statement? Well, this is why. We need an array with each vowel to check if the input string contains any fo this characters.
    

```typescript
const checker = ['a', 'e', 'i', 'o', 'u'];
```

* Next, we need to loop each character in the input string using a [for…of](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of).
    

```typescript
// convert to lowerCase to prevent mismatch
for(let char of str.toLowerCase()) {}
```

* We need to check if the `char` is part of our checker. The vowels, and for this we are going to use the [includes method](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/includes).
    

```typescript
if(checker.includes(char))
```

* If `checker` includes `char` : if the character is a vowel in simple words, increment the `count` variable. Otherwise, continue with the next iteration.
    

```typescript
if(checker.includes(char)){
    // the char is a vowel
    count++;
}
```

* Return the count of vowels in the input string.
    

```typescript
return count;
```

As you can see this is an easy one, but a helpful to master the basics, since we covered strings manipulation, array methods and loops. So, if you are starting in CS, it is a good starting point.

#### Typescript Implementation

```tsx
export function vowels(str: string): number{
    let count = 0;
    const checker = ['a', 'e', 'i', 'o', 'u'];
    for(let char of str.toLowerCase()) {
        if(checker.includes(char)) {
            count++;
        }
    }
    return count;
}
```

#### Conclusion

Voila! Now you know how to count vowels in a string. For an extra challenge, consider: how would you modify this code to count each vowel separately? That is, counting how many `a`'s, `e`'s, and so on.

As you can see, learning algorithms isn’t rocket science, but it requires patience and, most importantly, a clear path. You need to master the basics and build from there — otherwise, you’ll just memorize solutions without understanding the logic behind them.

And remember, you can check this and other algorithms in my [repo](https://github.com/RubenOAlvarado/algorithms). I’m planning to include them in other languages.

In our next post, we’ll explore the word count algorithm. Stay tuned!