Lecture 12

Multidimensional Arrays

Arrays in C can have multiple subscripts. A common use of multiple subscripted arrays is to represent tables of values consisting of information arranged in rows and columns. To identify a particular table element, we must specify two subscripts: the first identifies the row and the second identifies the column. Arrays that require two subscripts to identify a particular element are called double subscripted arrays. Note that, multidimensional arrays can have more than two subscripts. ANSI standard supports at least 12 subscripts.

When we say a 3X4 array, we declare it as follows-

int a [3][4];

When we declare in such a way, the actual thing that takes place in memory is illustrated below-

a [0] [0]	a [0] [1]	a [0] [2]	a [0] [3]
a [1] [0]	a [1] [1]	a [1] [2]	a [1] [3]
a [2] [0]	a [2] [1]	a [2] [2]	a [2] [3]

So, the first subscript denotes the row and the second subscript denotes the column.

A multiple subscripted array can be initialized in its declaration much like a subscripted array. b [2] [2] can be declared and initialized like

int b [2] [2] = {{1,2}, {3,4}};

in that case, 1 and 2 initialize b[0][0] and b[0][1] and 3 and 4 initialize b[1][0] and b[1][1].

Let’s demonstrate the stuff with an example. We will declare three 2X3 arrays- array1, array2 and array3. Thereafter, we will put values into those arrays in several different ways.

main(){

int array1 [2][3]={{1,2,3},{4,5,6}};

int array2 [2][3]={1,2,3,4,5};

int array3 [2][3]={{1,2},{4}};

printf(“Values in array1 are: \n”);

for(int i=0;i<=1;i++){ // taking track of rows

for (int j=0;j<=2;j++) //taking track of columns

printf (“%d ”, array1[i][j]);

printf(“\n”);

}

printf(“Values in array2 are: \n”);

for(int i=0;i<=1;i++){ // taking track of rows

for (int j=0;j<=2;j++) //taking track of columns

printf (“%d ”, array2[i][j]);

printf(“\n”);

}

printf(“Values in array3 are: \n”);

for(int i=0;i<=1;i++){ // taking track of rows

for (int j=0;j<=2;j++) //taking track of columns

printf (“%d ”, array3[i][j]);

printf(“\n”);

}

The output of the program is-

Values in array1 are:

1 2 3

4 5 6

Values in array2 are:

1 2 3

4 5 0

Values in array3 are:

1 2 0

4 0 0

To understand more deeply how the values are stored in a two dimensional array, let us consider another example-

main(){

int a [4][5];

int i, j;

for(i=0;i<=4;i++)

for (j=0;j<=5;j++)

a[i][j]=i*j;

for(i=0;i<=4;i++){

for (j=0;j<=5;j++)

printf(“%d ”, a[i][j]);

printf(“\n”);

}

The output of the program is-

0 0 0 0 0

0 1 2 3 4

0 2 4 6 8

0 3 6 9 12

It is important to remember that while initializing a 2-D array it is necessary to mention the second (column) dimension, whereas the first dimension (row) is optional.

Thus the declarations,

are perfectly valid.

But declarations like

are not valid.

Three Dimensional Array

We aren’t going to show a programming example that uses a three-dimensional array. This is because, in practice, one rarely uses this array. However, an example of initializing a three-dimensional array will consolidate your understanding of subscripts:

This three dimensional array can be thought of array or array of array. In other word, 3 pieces of 4X2 arrays.

Passing Arrays to Functions

Array elements can be passed to a function by calling the function by value, or by reference. In the call by value we pass values of array elements to the function, whereas in the call by reference we pass addresses of array elements to the function. As we did not see call by reference yet, we will see that later.

and the output is

Here, we are passing an individual array element at a time to the function display( ) and getting it printed in the function display( ). Note that since at a time only one element is being passed, this element is collected in an ordinary integer variable m, in the function display( ).

Now we will take a loot at an example that passes a two dimensional array to a function-