Jagged Array or Array of Arrays in C with Examples

Prerequisite: Arrays in C

Jagged array is array of arrays such that member arrays can be of different sizes, i.e., we can create a 2-D array but with a variable number of columns in each row. These type of arrays are also known as Jagged arrays.

Example:

arr[][] = { {0, 1, 2},
            {6, 4},
            {1, 7, 6, 8, 9},
            {5} 
          };

Below are the methods to implement the jagged array in C:



  1. Using array and a pointer (Static Jagged Array)
    • First declare 1-D arrays with the number of rows you will need,
    • The size of each array (array for the elements in the row) will be the number of columns (or elements) in the row,
    • Then declare a 1-D array of pointers that will hold the addresses of the rows,
    • The size of the 1-D array is the number of rows you want in the jagged array.

    Below is the implementation of the above approach:
    Example:

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    // C program to show the
    // implementation of Jagged Arrays
      
    #include <stdio.h>
    #include <stdlib.h>
      
    int main()
    {
      
        int row0[4] = { 1, 2, 3, 4 };
        int row1[2] = { 5, 6 };
      
        int* jagged[2] = { row0, row1 };
      
        // Array to hold the size of each row
        int Size[2] = { 4, 2 }, k = 0;
      
        // To display elements of Jagged array
        for (int i = 0; i < 2; i++) {
      
            // pointer to hold the address of the row
            int* ptr = jagged[i];
      
            for (int j = 0; j < Size[k]; j++) {
                printf("%d ", *ptr);
      
                // move the pointer to the
                // next element in the row
                ptr++;
            }
      
            printf("\n");
            k++;
      
            // move the pointer to the next row
            jagged[i]++;
        }
      
        return 0;
    }

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    Output:

    1 2 3 4 
    5 6
    
  2. Using an array of pointer (Dynamic Jagged Array)
    • Declare an array of pointers (jagged array),
    • The size of this array will be the number of rows required in the Jagged array
    • Then for each pointer in the array allocate memory for the number of elements you want in this row.

    Below is the implementation of the above approach:
    Example:

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    // C program to show the
    // implementation of Jagged Arrays
      
    #include <stdio.h>
    #include <stdlib.h>
      
    int main()
    {
        // 2 Rows
        int* jagged[2];
      
        // Allocate memory for elements in row 0
        jagged[0] = malloc(sizeof(int) * 1);
      
        // Allocate memory for elements in row 1
        jagged[1] = malloc(sizeof(int) * 3);
      
        // Array to hold the size of each row
        int Size[2] = { 1, 3 }, k = 0, number = 100;
      
        // User enters the numbers
        for (int i = 0; i < 2; i++) {
      
            int* p = jagged[i];
      
            for (int j = 0; j < Size[k]; j++) {
                *p = number++;
      
                // move the pointer
                p++;
            }
            k++;
        }
      
        k = 0;
      
        // Display elements in Jagged array
        for (int i = 0; i < 2; i++) {
      
            int* p = jagged[i];
            for (int j = 0; j < Size[k]; j++) {
      
                printf("%d ", *p);
                // move the pointer to the next element
                p++;
            }
            printf("\n");
            k++;
            // move the pointer to the next row
            jagged[i]++;
        }
      
        return 0;
    }

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    Output:

    100 
    101 102 103
    

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