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# Arrays

## **What is an Array?**

An array is a **sequence of elements** that are stored in **contiguous memory locations**. Each element in the array is of the **same data type**, and you can access them using an **index**.

**Key Points:**

* All elements in an array are of the same type (e.g., all integers, all floats).
* The **index** of an array starts at `0`.
* Arrays are **fixed in size**, meaning you must define the size when you declare the array.

***

#### **Array Declaration and Initialization**

To declare an array, you specify the type, the name, and the number of elements (size). You can also initialize the array with values.

**Syntax:**

```c
type arrayName[arraySize];
```

**Example:**

```c
int numbers[5];  // Declares an array 'numbers' that can hold 5 integers
```

***

#### **Array Initialization**

You can initialize an array when you declare it by listing its values in curly braces `{}`.

**Example:**

```c
int numbers[5] = {10, 20, 30, 40, 50};  // Array with 5 elements
```

* The array `numbers` holds the values `10, 20, 30, 40, 50`.

If you don’t initialize all the elements, the remaining elements are automatically set to `0`.

**Example:**

```c
int numbers[5] = {1, 2};  // The first two elements are 1 and 2, rest are 0
```

***

#### **Accessing Elements in an Array**

You can access array elements using their index. Remember, the first element has an index of `0`.

**Syntax:**

```c
arrayName[index];
```

**Example:**

```c
int numbers[5] = {10, 20, 30, 40, 50};
printf("%d\n", numbers[0]);  // Outputs 10
printf("%d\n", numbers[4]);  // Outputs 50
```

***

#### **Modifying Elements**

You can change the value of a specific element by assigning it a new value.

**Example:**

```c
int numbers[5] = {10, 20, 30, 40, 50};
numbers[2] = 100;  // Change the value at index 2 to 100
printf("%d\n", numbers[2]);  // Outputs 100
```

***

#### **Looping through Arrays**

Using loops, especially `for` loops, is the easiest way to work with arrays.

**Example:**

```c
int numbers[5] = {10, 20, 30, 40, 50};

for (int i = 0; i < 5; i++) {
    printf("%d\n", numbers[i]);
}
```

* This loop prints all the elements of the `numbers` array.

***

#### **Multidimensional Arrays**

C allows you to create arrays with more than one dimension. A **two-dimensional array** can be thought of as a grid or matrix.

**Syntax:**

```c
type arrayName[rows][columns];
```

**Example:**

```c
int matrix[2][3] = {
    {1, 2, 3}, 
    {4, 5, 6}
};
```

* This creates a 2x3 array (2 rows and 3 columns).

You can access elements of a 2D array like this:

```c
printf("%d\n", matrix[0][1]);  // Outputs 2 (row 0, column 1)
```

***

#### **Practical Example: Sum of Array Elements**

Let’s sum all elements of an integer array.

```c
#include <stdio.h>

int main() {
    int numbers[5] = {10, 20, 30, 40, 50};
    int sum = 0;

    for (int i = 0; i < 5; i++) {
        sum += numbers[i];
    }

    printf("Sum of array elements: %d\n", sum);

    return 0;
}
```

* This code adds up the elements of the `numbers` array and prints the sum (`150` in this case).

***

#### **Arrays Summary**

| Concept                     | Explanation                                                                        |
| --------------------------- | ---------------------------------------------------------------------------------- |
| **Array Declaration**       | `type arrayName[size];` - Fixed size, elements stored in sequence.                 |
| **Indexing**                | Arrays are indexed starting from 0.                                                |
| **Initialization**          | Arrays can be initialized when declared (e.g., `{1, 2, 3}`) or left uninitialized. |
| **Access/Modification**     | Use `arrayName[index]` to access or modify elements.                               |
| **Looping Through Arrays**  | Use loops to iterate over elements (e.g., `for` loop).                             |
| **Multidimensional Arrays** | Arrays with more than one dimension (e.g., `int matrix[2][3]`).                    |

***