C two-dimensional array

It is also possible for arrays to have two or more dimensions. The two dimensional array is also called as a matrix. In C language two dimensional array is represented by rows and columns. It is also known as an array of arrays or list of arrays. This two dimensional array can be called as a multi dimensional array.

A pictorial representation of the 2-D array:

The following figure shows how data is stored in memory in matrix form:

Declaration of two dimensional array:

For example: int arr[4][3];
Here the first dimension always represents a row and the second dimension represents a column. In above example 4 is the row number and 3 is a column number. An arr is an array of data type int.

Initialisation of Two-Dimensional Array:

You can initialise two dimensional array in any of the following two ways:

This example is represented in matrix form as follow:

Points to remember:

• You can skip row size. But it is mandatory to give column size.
  
  int a[][2] = {{1,2}, {3,4}, {5,6}};

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

  It is represented as follow:

  1 2 3 4 5 6

  1 2 3

  1 2 3 4 5 6

• int[3][3] = {{1}, {4}, {7}};

  1	int[3][3] = {{1}, {4}, {7}};

  This is represented as follow:

  1 0 0 4 0 0 7 0 0

  1 2 3

  1 0 0 4 0 0 7 0 0

• int a[][3] = {1, 2, 3, 4, 5, 6};

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

  It is represented as:

  1 2 3 4 5 6

  1 2	1 2 3 4 5 6

• Empty brackets are not allowed.
  int[3][3] = {{1}, {4}, {7}, {}}; //error

  1	int[3][3] = {{1}, {4}, {7}, {}};    //error

• Following initilisations are not valid.
  • column size is not given so it is invalid.
    int xyz[][] = {{1,2}, {3,4}, {5,6}};         //error

    1	int xyz[][] = {{1,2}, {3,4}, {5,6}};         //error

  • int pqr[2][]={{1,2},{3,4},{5,6}};     //error

    1	int pqr[2][]={{1,2},{3,4},{5,6}};     //error

  • Variable name is not allowed as row_size or column_size:
    int row=3; column=3; int a[row][column]={{1,2},{3,4},{5,6}}; //error

    1 2	int row=3; column=3; int a[row][column]={{1,2},{3,4},{5,6}};  //error

  • int arr[4][3]={1,2,3,2,5,6,8,4,3,5,1,9}; printf("%d", sizeof(a)); //48 bytes

    1 2	int arr[4][3]={1,2,3,2,5,6,8,4,3,5,1,9}; printf("%d", sizeof(a));   //48 bytes

    Since array is are of integer type and contain 12 elements. Therefore (4*3)*4=48 bytes(i.e number of rows * number of columns)

  Accessing 2-D array elements using subscripts-

  int var = a[2][3];

  1	int var = a[2][3];

  The 4th element from 3rd row of the array is assign to var. In this way, we can access any element from array.
  Address of an element can be written as:

  address = *(array_name + rows x sizeof(data_type))+column x sizeof(data_type)
  &a[i][j] = *(a + i) + j
  & arr[0][1] = *((arr + 1 x 4)+1 x 4) = 104

  For example:

  #include<stdio.h> int main() { int array[2][2] = {58, 96, 66, 30}; //To get first element printf("first element is = %d", array[0][0]); //58 //To get address of first element printf("address of first element is = %d", array); //2000 printf("address of first element is = %d", (array + 0)); //2000 printf("address of first element is = %d", (0+array)); //2000 //To get second element printf("second element is = %d", array[0][1]); //96 //To get address of second element printf("address of second element is = %d", (array + 1)); //2004 printf("address of second element is = %d", (1+array)); //2004 //To get third element printf("third element is = %d", array[1][0]); //66 //To get address of third element printf("address of third element is = %d", (array + 2)); //2008 printf("address of third element is = %d", (2+array)); //2008 //To get forth element printf("forth element is = %d", array[1][1]); //30 //To get address of forth element printf("address of forth element is = %d", (array + 2)); //2008 printf("address of forth element is = %d", (2+array)); //2008 }

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

  #include<stdio.h> int main() { int array[2][2] = {58, 96, 66, 30};   //To get first element printf("first element is = %d", array[0][0]);     //58   //To get address of first element printf("address of first element is = %d", array);       //2000 printf("address of first element is = %d", (array + 0)); //2000 printf("address of first element is = %d", (0+array));   //2000 //To get second element printf("second element is = %d", array[0][1]);    //96 //To get address of second element printf("address of second element is = %d", (array + 1)); //2004 printf("address of second element is = %d", (1+array));   //2004 //To get third element printf("third element is = %d", array[1][0]);   //66 //To get address of third element printf("address of third element is = %d", (array + 2)); //2008 printf("address of third element is = %d", (2+array));   //2008 //To get forth element printf("forth element is = %d", array[1][1]);   //30 //To get address of forth element printf("address of forth element is = %d", (array + 2)); //2008 printf("address of forth element is = %d", (2+array));   //2008 }

  Example of 2-D Array in C

  #include<stdio.h> int main() { int i=0, j=0; int arr[4][3]={{1,2,3},{2,3,4},{3,4,5},{4,5,6}}; //traversing 2D array for(i=0; i < 4; i++) { for(j=0; j < 3; j++) { printf("arr[%d][%d]=%d\n", i, j, arr[i][j]); } } }

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

  #include<stdio.h> int main() {   int i=0, j=0;   int arr[4][3]={{1,2,3},{2,3,4},{3,4,5},{4,5,6}};   //traversing 2D array   for(i=0; i < 4; i++)   {     for(j=0; j < 3; j++)     {      printf("arr[%d][%d]=%d\n", i, j, arr[i][j]);     }   } }

  
  Output:
  
  arr[0][0] = 1 arr[0][1] = 2 arr[0][2] = 3 arr[1][0] = 2 arr[1][1] = 3 arr[1][2] = 4 arr[2][0] = 3 arr[2][1] = 4 arr[2][2] = 5 arr[3][0] = 4 arr[3][1] = 5 arr[3][2] = 6

  1 2 3 4 5 6 7 8 9 10 11 12

  arr[0][0] = 1 arr[0][1] = 2 arr[0][2] = 3 arr[1][0] = 2 arr[1][1] = 3 arr[1][2] = 4 arr[2][0] = 3 arr[2][1] = 4 arr[2][2] = 5 arr[3][0] = 4 arr[3][1] = 5 arr[3][2] = 6