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Two Dimensional Array in C

Last updated on July 27, 2020

Two-dimensional Array#

The syntax declaration of 2-D array is not much different from 1-D array. In 2-D array, to declare and access elements of a 2-D array we use 2 subscripts instead of 1.

Syntax:datatype array_name[ROW][COL];

The total number of elements in a 2-D array isROW*COL. Let’s take an example.

intarr[2][3];

This array can store2*3=6 elements. You can visualize this 2-D array as a matrix of 2 rows and 3 columns.

The individual elements of the above array can be accessed by using two subscript instead of one. The first subscript denotes row number and second denotes column number. As we can see in the above image both rows and columns are indexed from0. So the first element of this array is atarr[0][0] and the last element is atarr[1][2]. Here are how you can access all the other elements:

arr[0][0] - refers to the first element
arr[0][1] - refers to the second element
arr[0][2] - refers to the third element
arr[1][0] - refers to the fourth element
arr[1][1] - refers to the fifth element
arr[1][2] - refers to the sixth element

If you try to access an element beyond validROW andCOL , C compiler will not display any kind of error message, instead, a garbage value will be printed. It is the responsibility of the programmer to handle the bounds.

arr[1][3] - a garbage value will be printed, because the last valid index ofCOL is2
arr[2][3] - a garbage value will be printed, because the last valid index ofROW andCOL is1 and2 respectively

Just like 1-D arrays, we can only also use constants and symbolic constants to specify the size of a 2-D array.

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#define ROW 2#define COL 3inti=4,j=6;intarr[ROW][COL];// OKintnew_arr[i][j];// ERROR

Processing elements of a 2-D array#

To process elements of a 2-D array, we use two nested loop. The outer for loop to loop through all the rows and inner for loop to loop through all the columns. The following program will clear everything.

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#include<stdio.h>#define ROW 3#define COL 4intmain(){intarr[ROW][COL],i,j;for(i=0;i<ROW;i++){for(j=0;j<COL;j++){printf("Enter arr[%d][%d]: ",i,j);scanf("%d",&arr[i][j]);}}printf("\nEntered 2-D array is:\n\n");for(i=0;i<ROW;i++){for(j=0;j<COL;j++){printf("%3d ",arr[i][j]);}printf("\n");}// signal to operating system everything works finereturn0;}

Expected Output:

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Enter arr[0][0]: 11Enter arr[0][1]: 35Enter arr[0][2]: 73Enter arr[0][3]: 831Enter arr[1][0]: 3Enter arr[1][1]: 40Enter arr[1][2]: 31Enter arr[1][3]: 93Enter arr[2][0]: 35Enter arr[2][1]: 10Enter arr[2][2]: 52Enter arr[2][3]: 81Entered 2-D array is:11 35 73 8313 40 31 9335 10 52 81

How it works:

There is nothing new in this previous program that deserves any explanation. We are just using two nested for loops. The first nested for loop takes input from the user. And the second for loop prints the elements of a 2-D array like a matrix.

Initializing 2-D array#

Initialization of 2-D array is similar to a 1-D array. For e.g:

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inttemp[2][3]={{1,2,3},// row 0{11,22,33}// row 1};

After this initialization, each element is as follows:

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temp[0][0]:1temp[0][1]:2temp[0][2]:3temp[1][0]:11temp[1][1]:22temp[1][2]:33

Consider another initialization.

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intmy_arr[4][3]={{10},{77,92},{33,89,44},{12,11}};

The size ofmy_arr is4*3=12 , but in the initialization, we have only specified the value of8 elements. In such cases, the remaining elements will be given the value of0.

The individual elements are as follows:

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my_arr[0][0]:10my_arr[0][1]:0my_arr[0][2]:0my_arr[1][0]:77my_arr[1][1]:92my_arr[1][2]:0my_arr[2][0]:33my_arr[2][1]:89my_arr[2][2]:44my_arr[3][0]:12my_arr[3][1]:11my_arr[4][2]:0

In 2-D arrays, it is optional to specify the first dimension but the second dimension must always be present. This works only when you are declaring and initializing the array at the same time. For example:

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inttwo_d[][3]={{13,23,34},{15,27,35}};

is same as

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inttwo_d[2][3]={{13,23,34},{15,27,35}};

As discussed earlier you can visualize a 2-D array as a matrix. The following program demonstrates the addition of two matrices.

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#include<stdio.h>#define ROW 2#define COL 3intmain(){intmat1[ROW][COL],mat2[ROW][COL],mat3[ROW][COL];inti,j;printf("Enter first matrix:\n\n");for(i=0;i<ROW;i++){for(j=0;j<COL;j++){printf("Enter a[%d][%d]: ",i,j);scanf("%d",&mat1[i][j]);}}printf("\nEnter Second matrix:\n\n");for(i=0;i<ROW;i++){for(j=0;j<COL;j++){printf("Enter a[%d][%d]: ",i,j);scanf("%d",&mat2[i][j]);}}// add mat1 and mat2for(i=0;i<ROW;i++){for(j=0;j<COL;j++){mat3[i][j]=mat1[i][j]+mat2[i][j];}}printf("\nResultant array:\n\n");// print resultant arrayfor(i=0;i<ROW;i++){for(j=0;j<COL;j++){printf("%5d ",mat3[i][j]);}printf("\n");}// signal to operating system program ran finereturn0;}

Expected Output:

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Enter first matrix:Enter a[0][0]: 12Enter a[0][1]: 32Enter a[0][2]: 13Enter a[1][0]: 35Enter a[1][1]: 54Enter a[1][2]: 35Enter Second matrix:Enter a[0][0]: 57Enter a[0][1]: 64Enter a[0][2]: 58Enter a[1][0]: 72Enter a[1][1]: 84Enter a[1][2]: 29Resultant array:mat1 + mat2 =69 96 71107 138 64

How it works:

Two matrices can be added or subtracted, only if they have the same dimension. In other words, a matrix of size2*3 can be added to another matrix of 2*3, but you can’t add or subtract it to a matrix of2*4 or3*2. The resultant array will be a matrix of the same dimension as the original two. First two for loops asks the user to enter two matrices. The third for loop adds corresponding elements ofmat1 andmat2 in a new arraymat3. Fourth for loop prints the elements of arraymat3.

Arrays of more than two dimension#

You can even create an array of 3 or more dimensions or more, but generally, you will never need to do so. Therefore, we will restrict ourself to 3-D arrays only.

Here is how you can declare an array of 3 dimensions.

intarr[2][3][2];

3-D array uses three indexes or subscript. This array can store2*3*2=12 elements.

Here is how to initialize a 3-D array.

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intthree_d[2][3][4]={{{12,34,56,12},{57,44,62,14},{64,36,91,16},},{{87,11,42,82},{93,44,12,99},{96,34,33,26},}};

You can think of this array as 2 2-D arrays and each of these 2-D array has3 rows and4 columns;

Here are individual elements of the array:

First Row

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three_d[0][0][0] : 12three_d[0][0][1] : 34three_d[0][0][2] : 56three_d[0][0][3] : 12three_d[0][1][0] : 57three_d[0][1][1] : 44three_d[0][1][2] : 62three_d[0][1][3] : 14three_d[0][2][0] : 64three_d[0][2][1] : 36three_d[0][2][2] : 91three_d[0][2][3] : 16

Second Row

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three_d[1][0][0] : 87three_d[1][0][1] : 11three_d[1][0][2] : 42three_d[1][0][3] : 82three_d[1][1][0] : 93three_d[1][1][1] : 44three_d[1][1][2] : 12three_d[1][1][3] : 99three_d[1][2][0] : 96three_d[1][2][1] : 34three_d[1][2][2] : 33three_d[1][2][3] : 26

Passing Multidimensional Arrays to Functions#

You can pass multi-dimensional arrays to functions just like a 1-D array, but you need to specify the size of the all other dimensions except the first one. For e.g:

If you need to passarr[2][3] to a function calledfunc_1(), then you need to declare thefunc_1() like this:

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voidfunc_1(intmy_arr[2][3])// OK{//...}

or like this:

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voidfunc_1(intmy_arr[][3])// OK{//...}

It would be invalid to declare formal argument as follows:

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voidfunc_1(intmy_arr[][])// error{//...}

Similarly to pass a 3-D array you need to declare the function as follows:

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intarr[2][3][4];voidfunc_1(intmy_arr[][3][4]){//...}