# Problem 8: Count Vowels

Hey everyone! 👋

Today, we're tackling a string manipulation problem: **Counting Vowels**.

## **The Problem**

The goal is to write a function that counts the number of vowels in a given string. We need to consider both lowercase and uppercase vowels ('a', 'e', 'i', 'o', 'u').

**Example:**

* `count_vowels("hello world")` should return `3`
    
* `count_vowels("AEIOU")` should return `5`
    

## **The Solution**

Here is the Python implementation:

```python
def count_vowels(s):
    """
    Counts the number of vowels in a string.
    """
    vowels = {'a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'}
    count = 0
    for char in s:
        if char in vowels:
            count += 1
    return count

# Test case
print(count_vowels("pooopcycle"))
# Output: 4
```

## **Code Breakdown**

Let's walk through the code line by line:

1. `def count_vowels(s):`
    
    * Defines a function named `count_vowels` that takes one parameter `s` (a string).
        
2. `vowels = {'a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'}`
    
    * Creates a set containing all vowels (both lowercase and uppercase).
        
    * Using a set allows for efficient O(1) lookups.
        
3. `count = 0`
    
    * Initializes a counter variable `count` to 0.
        
4. `for char in s:`
    
    * Iterates through each character in the input string `s`.
        
5. `if char in vowels:`
    
    * Checks if the current character exists in the `vowels` set.
        
6. `count += 1`
    
    * If the character is a vowel, increments the `count` by 1.
        
7. `return count`
    
    * Returns the final count of vowels.
        

### **Example Walkthrough with** `"pooopcycle"`

1. `char` is 'p', not in vowels.
    
2. `char` is 'o', in vowels -> `count` becomes 1.
    
3. `char` is 'o', in vowels -> `count` becomes 2.
    
4. `char` is 'o', in vowels -> `count` becomes 3.
    
5. `char` is 'p', not in vowels.
    
6. `char` is 'c', not in vowels.
    
7. `char` is 'y', not in vowels.
    
8. `char` is 'c', not in vowels.
    
9. `char` is 'l', not in vowels.
    
10. `char` is 'e', in vowels -> `count` becomes 4.
    
11. Returns `4`.
    

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Happy coding! 💻