# Arrays and Lists

Arrays and Lists are fundamental data structures used to store collections of data. They allow you to hold multiple values under a single variable name, organized by an index.

## 1. Arrays vs. Lists

While often used interchangeably in conversation, there is a technical distinction in computer science:

*   **Arrays:** Typically have a **fixed size** and store elements of the **same data type**. They are stored in contiguous memory locations. (Common in C, C++, Java).
*   **Lists (Dynamic Arrays):** Can grow or shrink in size dynamically and often hold elements of **mixed data types**. (Common in Python, JavaScript, Ruby).

## 2. Declaration and Initialization

### JavaScript (Array)
JavaScript arrays are dynamic and can hold mixed types.
```javascript
let numbers = [1, 2, 3, 4, 5];
let mixed = ["Hello", 42, true];
```

### Python (List)
Python lists are dynamic and very flexible.
```python
numbers = [1, 2, 3, 4, 5]
fruits = ["apple", "banana", "cherry"]
```

### Java (Array)
Java arrays are fixed-size and strongly typed.
```java
// Size is fixed at initialization
int[] numbers = {1, 2, 3, 4, 5};
String[] names = new String[5]; // Empty array of size 5
```

## 3. Accessing Elements (Indexing)

Almost all modern programming languages use **0-based indexing**, meaning the first element is at index 0.

```javascript
let colors = ["Red", "Green", "Blue"];

console.log(colors[0]); // "Red"
console.log(colors[1]); // "Green"
```

## 4. Common Operations

### Getting the Length
*   **JavaScript:** `arr.length`
*   **Python:** `len(arr)`
*   **Java:** `arr.length`

### Adding Elements
*   **JavaScript:** `arr.push("New Item")`
*   **Python:** `arr.append("New Item")`
*   **Java:** Cannot add to a standard array (must use `ArrayList`).

### Iterating (Looping)
```python
# Python
for item in items:
    print(item)
```

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[[programming/control-flow]]