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:

   // 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;
   }
   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:

   // 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;
   }
   Output:

   100 
   101 102 103