# 2d arrays

## 🔹 Step 1: Introduction

👨‍🏫 *Teacher:*  
“Bachcho, aaj hum **2D Array in C** पढ़ेंगे.  
Pehle yaad करो 1D array kya hota hai?  
1D array ek line jaisa hota hai jisme elements side-by-side store hote hain.

But kabhi kabhi hume data ko **rows aur columns** ki form me store karna padta hai, jaise:

* Cricket score table
    
* Students ke marks in 3 subjects
    
* Chess board
    

👉 Tab hum use karte hain **2D Array**.”

---

## 🔹 Step 2: Definition

👨‍🏫 *Teacher:*  
“2D array is basically an **array of arrays**.  
Socho jaise ek table:

```plaintext
Row 0 → [ 10   20   30 ]
Row 1 → [ 40   50   60 ]
```

Yaha row aur column dono hote hain.”

---

## 🔹 Step 3: Declaration

👨‍🏫 *Teacher:*  
“Syntax:”

```plaintext
data_type array_name[rows][columns];
```

Example:

```plaintext
int marks[3][4];  // 3 rows, 4 columns
```

💡 Question for Students:  
👉 Agar maine `int arr[5][6];` banaya hai, to total kitne elements honge?  
Answer = 5 × 6 = 30 elements.

---

## 🔹 Step 4: Initialization

👨‍🏫 *Teacher:*  
“Array ko initialize karne ke 3 common tarike hote hain.”

### (i) Row-wise braces:

```plaintext
int a[2][3] = { {1,2,3}, {4,5,6} };
```

### (ii) Without braces:

```plaintext
int b[2][3] = {1,2,3,4,5,6};
```

### (iii) Partial initialization:

```plaintext
int c[2][3] = { {1}, {4,5} };
// Result = { {1,0,0}, {4,5,0} }
```

---

## 🔹 Step 5: Accessing Elements

👨‍🏫 *Teacher:*  
“Kisi bhi element ko access karne ka formula:”

```plaintext
arr[row][column]
```

Example:

```plaintext
printf("%d", a[1][2]);  
// Means → 2nd row, 3rd column
```

---

## 🔹 Step 6: Input/Output with Loops

👨‍🏫 *Teacher:*  
“Jab hume user se values leni hain aur print karni hain, to nested loop ka use hota hai.”

```plaintext
#include <stdio.h>
int main() {
    int arr[2][3];
    
    // Input
    printf("Enter 6 elements:\n");
    for(int i=0; i<2; i++) {
        for(int j=0; j<3; j++) {
            scanf("%d", &arr[i][j]);
        }
    }
    
    // Output
    printf("Matrix is:\n");
    for(int i=0; i<2; i++) {
        for(int j=0; j<3; j++) {
            printf("%d ", arr[i][j]);
        }
        printf("\n"); // row complete hone ke baad new line
    }
    return 0;
}
```

📌 *Teacher dry run:*

* Suppose input = 1 2 3 4 5 6
    
* Matrix banega:
    

```plaintext
1 2 3  
4 5 6
```

---

## 🔹 Step 7: Memory Representation

👨‍🏫 *Teacher:*  
“C me data **row-major order** me store hota hai.”

Example:

```plaintext
int a[2][3] = { {1,2,3}, {4,5,6} };
```

Memory:  
`1 2 3 4 5 6`

👉 Matlab pehle puri row-0 store hoti hai, fir row-1.

---

## 🔹 Step 8: Applications

👨‍🏫 *Teacher:*  
“2D arrays kaha use hote hain?

* Matrices solve karne me
    
* Tabular data (marks, sales report)
    
* Image processing (pixels row × column)
    
* Games (tic-tac-toe, chessboard)”
    

---

## 🔹 Step 9: Practice Questions

👨‍🏫 *Teacher to Class:*  
“Ab kuch important problems karte hain.”

1. Matrix ko row-wise aur column-wise print karo.
    
2. Transpose of matrix likho.
    
3. Har row aur column ka sum nikalo.
    
4. Kisi element ko search karo.
    
5. 2 matrices ka multiplication karo.
    

---

📢 *Teacher:*  
“Ab homework: Har problem ko ek-ek karke code karke try karo.  
Next class me hum **transpose aur sum of rows/columns** ka code detail me dry run karenge.”