C.Tutorial

2-D Array in C

A 2-Dimensional (2-D) array in C is an array of arrays, essentially representing a table or matrix. It stores elements in rows and columns, making it useful for storing tabular data like a grid or matrix.

Definition

A 2-D array is an array of arrays, where each element is accessed by two indices: one for the row and one for the column. The size of a 2-D array is determined by the number of rows and columns.

Syntax:

                        
data_type array_name[row_size][column_size];

Example 1: Declaring and Initializing a 2-D Array

                        
                            {%raw%}
#include <stdio.h>
int main() 
{
  int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}}; // Declare and initialize a 2-D array
            
  // Print elements of the array in matrix format
  printf("Matrix:\n");
  for (int i = 0; i < 2; i++) {
      for (int j = 0; j < 3; j++) {
          printf("%d ", matrix[i][j]); // Print elements in a row
      }
      printf("\n"); // Move to the next line after each row
 }
    return 0;
}
    
              {%endraw%}

Output

Matrix: 1 2 3 4 5 6

Accessing Array Elements

In a 2-D array, each element is accessed by two indices: the row index and the column index. The row index represents the row, and the column index represents the element's position within that row.

Example 2: Accessing Elements Using Nested Loops

                        
                            {%raw%}
#include <stdio.h>
int main() 
{
   int matrix[3][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
                
   // Printing the matrix
   printf("Matrix:\n");
   for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 3; j++) {
           printf("%3d ", matrix[i][j]); // Print each element with proper spacing
        }
        printf("\n"); // Move to the next row
    }
    return 0;
}
           {%endraw%}

Output

Matrix: 1 2 3 4 5 6 7 8 9

Example 3: Modifying Array Elements

                        
{%raw%}
#include <stdio.h>
int main() 
{
    int matrix[2][2] = {{10, 20}, {30, 40}};
            
    // Modify an element in the array
    matrix[0][1] = 99;
            
    // Print the modified matrix
    printf("Matrix:\n");
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 2; j++) {
            printf("%d ", matrix[i][j]);
        }
          printf("\n"); // Move to the next row
    } 
        return 0;
    }
    
{%endraw%}

Output

Matrix: 10 99 30 40

Example 3: Modifying Array Elements

 
{%raw%}
#include <stdio.h>
int main() 
{

    int rows, cols, i, j;
    
    // Input the number of rows and columns
    printf("Enter the number of rows: ");
    scanf("%d", &rows);
    printf("Enter the number of columns: ");
    scanf("%d", &cols);

    // Declare matrices
    int matrix1[rows][cols], matrix2[rows][cols], sum[rows][cols];

    // Input the first matrix
    printf("Enter elements of the first matrix:\n");
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            printf("Element [%d][%d]: ", i + 1, j + 1);
            scanf("%d", &matrix1[i][j]);
        }
    }

    // Input the second matrix
    printf("Enter elements of the second matrix:\n");
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            printf("Element [%d][%d]: ", i + 1, j + 1);
            scanf("%d", &matrix2[i][j]);
        }
    }

    // Calculate the sum of the matrices
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            sum[i][j] = matrix1[i][j] + matrix2[i][j];
        }
    }

    // Display the resulting sum matrix
    printf("The resulting matrix after addition is:\n");
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            printf("%d ", sum[i][j]);
        }
        printf("\n");
    }
    return 0;
}
    
    
{%endraw%}

Output

Matrix: 10 99 30 40

Example 4: addition of two 2-dimensional arrays

 
{%raw%}
#include <stdio.h>
int main() 
{
    int rows, cols;
        
    // Input the dimensions of the matrices
    printf("Enter the number of rows: ");
    scanf("%d", &rows);
    printf("Enter the number of columns: ");
    scanf("%d", &cols);
    
    // Declare matrices
    int matrix1[rows][cols], matrix2[rows][cols], sum[rows][cols];
    
    // Input elements of the first matrix
    printf("Enter elements of the first matrix:\n");
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            printf("Enter element [%d][%d]: ", i + 1, j + 1);
            scanf("%d", &matrix1[i][j]);
        }
    }
    
    // Input elements of the second matrix
    printf("Enter elements of the second matrix:\n");
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            printf("Enter element [%d][%d]: ", i + 1, j + 1);
            scanf("%d", &matrix2[i][j]);
        }
    }
    
    // Calculate the sum of the matrices
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            sum[i][j] = matrix1[i][j] + matrix2[i][j];
        }
    }
    
    // Display the result
    printf("Resultant Matrix (Sum):\n");
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            printf("%d\t", sum[i][j]);
        }
        printf("\n");
    }
        
    return 0;
}
    
    
{%endraw%}

Output

Enter the number of rows: 2 Enter the number of columns: 2 Enter elements of the first matrix: Enter element [1][1]: 1 Enter element [1][2]: 2 Enter element [2][1]: 3 Enter element [2][2]: 4 Enter elements of the second matrix: Enter element [1][1]: 5 Enter element [1][2]: 6 Enter element [2][1]: 7 Enter element [2][2]: 8 Resultant Matrix (Sum): 6 8 10 12

Example 5: multiplication of two 2-dimensional arrays

 
{%raw%}
#include <stdio.h>
int main() 
{
    int rows1, cols1, rows2, cols2;
    
    // Input dimensions of the first matrix
    printf("Enter the number of rows for the first matrix: ");
    scanf("%d", &rows1);
    printf("Enter the number of columns for the first matrix: ");
    scanf("%d", &cols1);

    // Input dimensions of the second matrix
    printf("Enter the number of rows for the second matrix: ");
    scanf("%d", &rows2);
    printf("Enter the number of columns for the second matrix: ");
    scanf("%d", &cols2);

    // Check if multiplication is possible
    if (cols1 != rows2) {
        printf("Matrix multiplication is not possible. The number of columns in the first matrix must equal the number of rows in the second matrix.\n");
        return 1;
    }

    // Declare matrices
    int matrix1[rows1][cols1], matrix2[rows2][cols2], result[rows1][cols2];

    // Initialize the result matrix with zeros
    for (int i = 0; i < rows1; i++) {
        for (int j = 0; j < cols2; j++) {
            result[i][j] = 0;
        }
    }   
    
    // Input elements of the first matrix
    printf("Enter elements of the first matrix:\n");
    for (int i = 0; i < rows1; i++) {
        for (int j = 0; j < cols1; j++) {
            printf("Enter element [%d][%d]: ", i + 1, j + 1);
            scanf("%d", &matrix1[i][j]);
        }
    }

    // Input elements of the second matrix
    printf("Enter elements of the second matrix:\n");
    for (int i = 0; i < rows2; i++) {
        for (int j = 0; j < cols2; j++) {
            printf("Enter element [%d][%d]: ", i + 1, j + 1);
            scanf("%d", &matrix2[i][j]);
        }
    }

    // Perform matrix multiplication
    for (int i = 0; i < rows1; i++) {
        for (int j = 0; j < cols2; j++) {
            for (int k = 0; k < cols1; k++) {
                result[i][j] += matrix1[i][k] * matrix2[k][j];
            }
        }
    }

    // Display the result matrix
    printf("Resultant Matrix (Multiplication):\n");
    for (int i = 0; i < rows1; i++) {
        for (int j = 0; j < cols2; j++) {
            printf("%d\t", result[i][j]);
        }
        printf("\n");
    }   
    
    return 0;
}
    
    
{%endraw%}

Output

Enter the number of rows: 2 Enter the number of rows for the first matrix: 2 Enter the number of columns for the first matrix: 3 Enter the number of rows for the second matrix: 3 Enter the number of columns for the second matrix: 2 Enter elements of the first matrix: 1 2 3 4 5 6 Enter elements of the second matrix: 7 8 9 10 11 12 Resultant Matrix (Multiplication): 58 64 139 154

Example 6:Program for Transposing a Matrix

 
{%raw%}
#include <stdio.h>
int main() 
{
    int r, c, a[100][100], transpose[100][100], i, j;
    
    // Input rows and columns
    printf("Enter the number of rows (between 1 and 100): ");
    scanf("%d", &r);
    printf("Enter the number of columns (between 1 and 100): ");
    scanf("%d", &c);

    // Input elements of the matrix
    printf("nEnter elements of the matrix:\n");
    for (i = 0; i < r; ++i)
        for (j = 0; j < c; ++j) {
            printf("Enter element a%d%d: ", i + 1, j + 1);
            scanf("%d", &a[i][j]);
        }

    // Transpose the matrix
    for (i = 0; i < r; ++i)
        for (j = 0; j < c; ++j) {
            transpose[j][i] = a[i][j];
        }

    // Print the original matrix
    printf("nOriginal Matrix:\n");
    for (i = 0; i < r; ++i) {
        for (j = 0; j < c; ++j) {
            printf("%d   ", a[i][j]);
        }
        printf("\n");
    }       
    
    // Print the transposed matrix
        printf("nTransposed Matrix:\n");
        for (i = 0; i < c; ++i) {
            for (j = 0; j < r; ++j) {
                printf("%d   ", transpose[i][j]);
            }
            printf("\n");
        }    
    
    return 0;
}
      
{%endraw%}

Output

Enter the number of rows (between 1 and 100): 2 Enter the number of columns (between 1 and 100): 3 Enter elements of the matrix: Enter element a11: 1 Enter element a12: 2 Enter element a13: 3 Enter element a21: 4 Enter element a22: 6 Enter element a23: 7 Original Matrix: 1 2 3 4 6 7 Transposed Matrix: 1 4 2 6 3 7

Key Points:

Indexing:
- 2D arrays are indexed with two indices: [row][column].
- Example: arr[1][2] accesses the element at the second row, third column.
Initialization:
- You can initialize a 2D array statically when declaring it.
- Example: int arr[2][3] = {% raw %}{{1, 2, 3}, {4, 5, 6}}{% endraw %};
Memory Representation:
- 2D arrays are stored in row-major order in memory (i.e., all elements of one row are stored contiguously).
Dynamic 2D Arrays:
- You can create 2D arrays dynamically using pointers, but this requires dynamic memory allocation with malloc() or calloc().