Relation between Pointers and Arrays

Q: Briefly discuss the relation between pointers and arrays, giving suitable example. Write a program in C, to print transpose of a 2D matrix entered by a user. Also give comments  

Relation Between Pointers and Arrays in C:

In C, arrays and pointers are closely related because the name of an array represents the address of the first element of the array. An array's name can be used as a pointer to the first element, and you can access array elements using pointer arithmetic.

Key Points:

1. Array Name as Pointer: The name of an array is a constant pointer to the first element.
   • arr in int arr[3] is equivalent to &arr[0].
2. Pointer Arithmetic: Using pointers, you can traverse arrays by incrementing or decrementing the pointer.
   • *(arr + i) is equivalent to arr[i].
3. Accessing Array Elements: Both array indexing and pointer dereferencing can be used to access the elements of the array.

Example:

#include 
int main() {
    int arr[3] = {10, 20, 30};
    int *ptr = arr;  // Pointer to the first element of arr
    
    printf("Using pointer to access array elements:\n");
    
    // Access elements using pointer arithmetic
    for (int i = 0; i < 3; i++) {
        printf("Element %d: %d\n", i, *(ptr + i));  // *(ptr + i) is equivalent to arr[i]
    }
    
    return 0;
}

Output:

Using pointer to access array elements:
Element 0: 10
Element 1: 20
Element 2: 30

In the above code:

• ptr is a pointer to the first element of arr.
• We access each element of the array using pointer arithmetic, i.e., *(ptr + i).

C Program to Print the Transpose of a 2D Matrix:

Transpose of a Matrix: The transpose of a matrix is obtained by swapping its rows and columns. For example, the element at position [i][j] in the original matrix becomes the element at position [j][i] in the transposed matrix.

Code to Print Transpose of a 2D Matrix:

#include 
#define MAX 10  // Maximum size of the matrix
// Function to print the matrix
void printMatrix(int matrix[MAX][MAX], int rows, int cols) {
    for (int i = 0; i < rows>        for (int j = 0; j < cols>            printf("%d ", matrix[i][j]);
        }
        printf("\n");
    }
}
// Function to compute the transpose of the matrix
void transposeMatrix(int matrix[MAX][MAX], int transpose[MAX][MAX], int rows, int cols) {
    for (int i = 0; i < rows>        for (int j = 0; j < cols>            transpose[j][i] = matrix[i][j];  // Swap rows and columns
        }
    }
}
int main() {
    int matrix[MAX][MAX], transpose[MAX][MAX];
    int rows, cols;
    
    // Input the matrix dimensions
    printf("Enter the number of rows: ");
    scanf("%d", &rows);
    printf("Enter the number of columns: ");
    scanf("%d", &cols);
    
    // Input the matrix elements
    printf("Enter the elements of the matrix:\n");
    for (int i = 0; i < rows>        for (int j = 0; j < cols>            scanf("%d", &matrix[i][j]);
        }
    }
    
    // Display the original matrix
    printf("\nOriginal Matrix:\n");
    printMatrix(matrix, rows, cols);
    
    // Compute the transpose of the matrix
    transposeMatrix(matrix, transpose, rows, cols);
    
    // Display the transposed matrix
    printf("\nTranspose of the Matrix:\n");
    printMatrix(transpose, cols, rows);  // Transposed matrix has flipped dimensions
    
    return 0;
}

Explanation:

1. Input the Matrix: The user is prompted to enter the dimensions (rows and columns) of the matrix, followed by the matrix elements.
2. Transpose Calculation: The transposeMatrix() function swaps rows and columns of the input matrix.
   • The element at position [i][j] in the original matrix is moved to [j][i] in the transposed matrix.
3. Printing the Matrices: The printMatrix() function is used to print both the original and transposed matrices.

Example:

Input:

Enter the number of rows: 2
Enter the number of columns: 3
Enter the elements of the matrix:
1 2 3
4 5 6

Output:

Original Matrix:
1 2 3 
4 5 6 

Transpose of the Matrix:
1 4 
2 5 
3 6

Summary:

• This program demonstrates the use of arrays to store 2D matrices.
• The transpose of the matrix is achieved by swapping the rows and columns.
• The program makes use of nested loops to handle both input and the transpose operation.