# Data Structure & Alogrithm Lab

1.  What is an Array?
    

**Array** ek aisa data structure hai jisme **same data type ke multiple elements** ko ek hi naam ke under store kiya jata hai.

Example:

```c
int a[5];
```

Iska matlab hai:

*   `a` → array ka naam
    
*   `int` → data type ( Int, String, Boolean etc )
    
*   `[5]` → maximum **5 integer elements**
    

Index → elements ko identify/access karne ke liye use hota hai.

C language mein **index hamesha 0 se start hota hai**.

| Element | Index | Reference |
| --- | --- | --- |
| 1st | 0 | `a[0]` |
| 2nd | 1 | `a[1]` |
| 3rd | 2 | `a[2]` |
| 4th | 3 | `a[3]` |
| 5th | 4 | `a[4]` |

In simple Last index = **Array Length − 1**

## Arrays Can Store Different Data Types

Array sirf `int` ka hi nahi hota. Different data types ke arrays bana sakte hain.

### Integer Array

```c
int marks[5];
```

### Character Array

```c
char name[20];
```

### Float Array

```c
float price[10];
```

### Structure Array

```c
struct Student students[50];
```

Lets do the code

```c
#include <stdio.h> /*for Standard Input Output.*/

int main()
{
    int a[2] = {10, 20, 30};

    printf("First element = %d\n", a[0]); /*printf() → to display output*/
    printf("Second element = %d\n", a[1]);
    printf("Third element = %d\n", a[2]);

    return 0;
}
```

scanf() **→ to take input**

**printf() → to display output**

1.  Array Declaration
    

```c
int a[3] = {10, 20, 30};
```

This is the **most important line** for understanding arrays.

*   `int`
    

```c
int
```

It means the array will store **integer values**.

*   `a`
    

```plaintext
a
```

This is the **name of the array**.

*   `[3]`
    

```plaintext
[3]
```

This means the array can store **3 elements**.

*   `{10, 20, 30}`
    

These are the values stored inside the array.

So the array looks like this:

| Index | Value |
| --- | --- |
| `0` | `10` |
| `1` | `20` |
| `2` | `30` |

⚠️ Remember: **Array indexing starts from 0.**

### ⭐ Most Important Thing to Remember

If you write:

```c
int a[3] = {10, 20, 30};
```

There are **3 elements**, but the indexes are:

> **0, 1, 2**

Not:

> ❌ 1, 2, 3

1.  `return 0;`
    

```plaintext
return 0;
```

This tells the operating system:

> **The program finished successfully.** ✅

`0` generally indicates **successful execution**.

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## [**https://programiz.pro/code-visualizer/c**](https://programiz.pro/code-visualizer/c)

## Exam ke liye Important Points

1.  **Array is a collection of elements of the same data type.**
    
2.  Array elements ko **index** ke through access kiya jata hai.
    
3.  C language mein array indexing **0 se start hoti hai**.
    
4.  Last index = **length − 1**.
    
5.  `int a[5]` mein **5 elements** store ho sakte hain.
    
6.  `int a[5]` ke valid indexes **0, 1, 2, 3, 4** hain.
    
7.  `int b[5][6]` ek **two-dimensional array** hai.
    
8.  `b[5][6]` mein total **30 elements** ho sakte hain.
    
9.  2D array ka first element `b[0][0]` hota hai.
    
10.  2D array ka last element `b[4][5]` hota hai.
     
11.  Arrays `int`, `char`, `float`, `structure`, etc. ke ho sakte hain.
     

### 🧠Easy Trick

**C Array = Same Type + Same Name + Multiple Values + Index starts from 0**

```c
int a[5]

       0    1    2    3    4
      ↓    ↓    ↓    ↓    ↓
     [10] [20] [30] [40] [50]
```

`a[0]` **= first element**  
  
`a[4]` **= fifth/last element**