Arrays-Computer programming

ARRAYS
Need of an Array:
The variables of fundamental data types namely char,int,float,double can store only one value at
any given time. Therefore they can be used only to handle limited amounts of data. To process large
amount of data , we need a powerful data type that would facilitate efficient storing, accessing and
manipulation of data items. C supports a derived data type known as array that can be used for such
applications.
Array:
An array in C language is a collection of similar data-type, means an array can hold value of a
particular data type for which it has been declared.
Arrays can be created from any of the C data-types int, float, and char. So an integer array can
only hold integer values and cannot hold values other than integer. When we declare array, it allocates
contiguous memory location for storing values whereas 2 or 3 variables of same data-type can have
random locations. So this is the most important difference between a variable and an array.
Array Definition:
Array is a collection of variables, that can be stored in a continuous memory locations and shared a
common name.
(or)
Array by definition is a variable that hold multiple elements which has the same data type.
Arrays are of following types:
• Single dimensional arrays
• Double dimensional arrays
• Multi-dimension arrays.
Each of this array type can be of either static array or dynamic array. Static arrays have their
sizes declared from the start and the size cannot be changed after declaration. Dynamic arrays that allow
you to dynamically change their size at runtime, but they require more advanced techniques such as
pointers and memory allocation.
Single Dimension Arrays:
Declaring Single Dimension Arrays
Arrays can be declared using any of the data types available in C. Array size must be declared
using constant value before initialization. A single dimensional array will be useful for simple grouping of
data that is relatively small in size.

We can declare an array by specifying its data type, name and the fixed number of elements the array
holds between square brackets immediately following the array name.
The following illustrates how to declare an array:
data_type array_name[size];
For example, to declare an array that contains 100 integer numbers you can do as follows:
int a[100];
You must follow the rules below when you declare an array in C:
• The data type can be any valid C data types including C structure and union.
• The name of an array has to follow the rule of C variables.
• The size of array has to be a positive constant integer.
So far, we've been declaring simple variables: the declaration
int i;
Declares a single variable, named i, of type int. It is also possible to declare an array of several elements.
The declaration :
int a[10];
Declares an array, named a, consisting of ten elements, each of type int. Simply speaking, an array is a
variable that can hold more than one value. You specify which of the several values you're referring to at
any given time by using a numeric subscript OR index. (Arrays in programming are similar to vectors or
matrices in mathematics.) We can represent the array a above with a picture
Like this:
Initializing Single dimensional Arrays:
An array can be initialized at either of the flowing stages:’
• At compile time
• At run time

Compile time initialization:
It is like a variable, an array can be initialized. To initialize an array, you provide initializing values
which are enclosed within curly braces in the declaration and placed following an equals sign after the
array name.
Here is an examples of initializing an array of integers.
int a[5] = {2,1,3,7,8}; this declaration initialize the given 5 elements to an array a.
int arr[]={12,32,53,14,95}; this approach works fine as long as we initialize every element in the array
arr.
int a[5]={20,30,40}; this compile time initialization is partial. In such cases, the remaining elements are
initialized to zero.
char list[10]={‘a’,’e’,’i’}; this initialize first 3 position with a,e,i. and remaining all 7 positions to NULL.
int num[3]=(30,40,50,60}; we have more initializers than the declared size, the compiler will produce an
error. It is illegal in C.
The array initialization is done is given below
int a[5] = {12, 14, 16, 17, 18};
Here 5 elements are stored in an array ‘a’. The array elements are stored sequentially in separate
locations. Reading of array elements begins from ‘0’. Array elements are called by array names followed
by the element numbers. The 5 elements are referred as
Subscripted variable a[0] refers to the first element of array a, 12 i.e. a[0]=12
Subscripted variable a[4] refers to the first element of array a ,18 i.e. a[4]=18
If the array size is declared as 5. The elements are stored from index 0 to 4. i.e. If a[5] has been declared,
then values are stored from a[0] to a[4].
The integer enclosed in brackets is the array subscript, and its value must be in the range from
zero to one less than the number of memory cells in the array.

1) A simple ‘C’ program on Array Initialization Example
void main()
{
int arr[5],i;
clrscr();
arr[0]=10;
arr[1]=20;
arr[2]=30;
arr[3]=40;
arr[4]=50;
printf("Value in array arr[0] : %dn",arr[0]);
printf("n");
for(i=0;i<5;i++)
{
printf("Value in array arr[%d] : %dn",i,arr[i]);
}
}
Run time initialization:
An array can be explicitly initialized at run time. This approach is usually applied for initializing large
arrays. For example, consider the following segment of a C program.
-----------------
-----------------
for(i=0 ; i<10 ; i++)
a[i]=0;
The above runtime for loop statement initializes 0 to all 0-9 subscripts values of an array a[] , when the
program execution takes place.
Accessing Array Element from one-dimensional array:

You can access array elements via indexes like array_name[index].
Indexes of array starts from 0 not 1 so the highest elements of an array is array_name[size-1]
In C, arrays are zero-based: the ten elements of a 10-element array are numbered from 0 to 9.
The subscript which specifies a single element of an array is simply an integer expression in square
brackets. The first element of the array is a[0], the second element is a[1], etc. You can use these ``array
subscript expressions'' anywhere you can use the name of a simple variable, for example:
a[0] = 10;
a[1] = 20;
a[2] = a[0] + a[1];
We can access all the elements of an array with the following statements:
when we wanted to do something with a (such as print it out), the loop would run from 0 to n, where n is
not greater than the array size. (or whatever a's size was):
for(i = 0; i < n; i = i + 1)
printf("%dn", a[i]);
Sample Programs
/*A simple ‘C’ program to demonstrate the Runtime initialization and use of an array. */
main()
{
int i[10],j;
for ( j=0 ; j<10 ; j++)
i[j] = j ;
for ( j=0 ; j<10 ; j++)
printf("%d" , i[j]) ;
}
The above programs prints the output as 0 1 2 3 4 5 6 7 8 9.
1. /*Program to read an array of 10 numbers and print them */
void main()
{
int a[10],i;
clrscr();

printf("Enter 10 values :");
for(i=0; i<10; i++)
scanf("%d",&a[i]);
printf("Given Values :");
for(i=0; i<10; i++)
printf("%3d",a[i]);
}
Output
Enter 10 values ; 21 22 23 24 25 26 27 28 29 30
Given Values : 21 22 23 24 25 26 27 28 29 30
2./* Program to calculate the sum and average of six subject marks using arrays */
void main()
{
int a[10],i,sum=0;
float avg;
clrscr();
printf("Enter 6 subject marks :");
for(i=0; i<6; i++)
{
scanf("%d",&a[i]);
sum = sum + a[i];
}
printf("Sum = %d",sum);
avg= sum/6;
printf("nAvg = %f",avg);
}
Output
Enter 6 subject marks : 50 55 60 65 70 75
Sum = 375
Avg = 62.000000
3./* Program to calculate maximum and minimum of given numbers */
void main()
{
int a[100],n,max=0,min,i;
clrscr();
printf("Enter total numbers :");
scanf("%d",&n);
printf("Enter %d numbers :",n);
for(i=0; i<n; i++)
{
scanf("%d",&a[i]);
}
for(i=0; i<n; i++)
{
if(max<a[i])
max = a[i];
}
printf("Maximum Number = %d",max);
min=a[0];
for(i=0; i<n; i++)

{
if(min>a[i])
min = a[i];
}
printf("nMinimum Number = %d",min);
}
Output
Enter total numbers : 5
Enter 5 numbers : 16 32 03 15 12
Maximum Number = 32
Minimum Number = 36
Two Dimensional Arrays :
The array which is used to represent and store data in a tabular form is called as 'two
dimensional array.' Such type of array specially used to represent data in a matrix form.
The following syntax is used to represent two dimensional array.
Syntax:
<data-type> <array_name> [row_subscript][column-subscript];
Example:
int a[3][3];
In above example, a is an array of type integer which has storage size of 3 * 3 matrix. The total size
would be 3 * 3 * 2 = 18 bytes.
It is also called as 'multidimensional array.'
* Memory Allocation :
Fig : Memory allocation for two dimensional array
Initializing the Two-Dimensional arrays:
Compile time initializing of two-dimensional array:

We can initialize this 2D-array by writing:
int theArray[5][3] = { 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15 };
we can group the initializations with braces, as in the following example:
int theArray[5][3] = { {1,2,3},{4,5,6},{7,8,9},{10,11,12},{13,14,15} };
The compiler ignores the inner braces, which make it easier to understand how the numbers
are distributed. Each value must be separated by a comma, without regard to the braces. The entire
initialization set must be within braces, and it must end with a semicolon.
Int table[2][3]={ {1,1},(2}}; in this initialization the missing values are automatically set to 0.
All the elements can be initialized to zero by the following declaration:
Int m[3][5]={ {0},{0},{0}};
Runtime initialization of Two-Dimensional Arrays:
An two-dimensional array can be explicitly initialized at run time. This approach is usually applied for
initializing large arrays. For example, consider the following segment of a C program.
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
scanf("%d",&a[i][j]); //read 3*3 array
}
}
In this initialization the scanf functions reads the array elements in in a[][] by using two for loop
statements, and i,j are two subscripts of array a.
/*Program to demonstrate two dimensional array.*/
#include <stdio.h>
#include <conio.h>
void main()
{
int a[3][3], i, j;
clrscr();
printf("nt Enter matrix of 3*3 : ");
for(i=0; i<3; i++)
{

for(j=0; j<3; j++)
{
scanf("%d",&a[i][j]); //read 3*3 array
}
}
printf("nt Matrix is : n");
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
printf("t %d",a[i][j]); //print 3*3 array
}
printf("n");
}
getch();
}
Output :
Enter matrix of 3*3 : 3 4 5 6 7 2 1 2 3
Matrix is :
3 4 5
6 7 2
1 2 3
/* Program to read elements of two-dimensional array and print them in matrix format*/
void main()
{
int a[3][2],i,j;
clrscr();
printf("Enter elements of 3x2 matrix :");
for(i=0; i<3; i++)
{
for(j=0; j<2; j++)
{
scanf("%d",&a[i][j]);
}
}
printf("Given Elements are :n");
for(i=0; i<3; i++)
{
for(j=0; j<2; j++)
{
printf("%3d",a[i][j]);
}
printf("n");

}
}
Output
Enter elements of 3x2 matrix : 1 5 2 6 3 7
Given elements
1 5
2 6
3 7
/* Program to perform addition and subtraction of two matrices*/
void main()
{
int a[3][2],b[3][2],c[3][2],d[3][2],i,j;
clrscr();
printf("Enter elements of 3x2 matrix A:");
for(i=0; i<3; i++)
{
for(j=0; j<2; j++)
{
}
}
printf("Enter elements of 3x2 matrix B:");
for(i=0; i<3; i++)
{
for(j=0; j<2; j++)
{
scanf("%d",&b[i][j]);
}
}
for(i=0; i<3; i++)
{
for(j=0; j<2; j++)
{
c[i][j] = a[i][j] + b[i][j];
d[i][j] = a[i][j] - b[i][j];
}
}
printf("Resultant Sum Matrix :n");
for(i=0; i<3; i++)
{
for(j=0; j<2; j++)
{
printf("%3d",c[i][j]);
}
printf("n");
}
printf("Resultant Diff. Matrix :n");
for(i=0; i<3; i++)
{
for(j=0; j<2; j++)

{
printf("%3d",d[i][j]);
}
printf("n");
}
}
Output
Enter elements of 3x2 matrix A : 1 2 3 4 5 6
Enter elements of 3x2 matrix B : 7 8 9 0 1 2
Resultant Sum Matrix :
8 10
12 4
6 7
Resultant Diff. Matrix ;
-6 -6
-6 4
4 4
/* Program to perform multiplication of two matrices*/
void main()
{
int a[3][2],b[2][3],c[3][3],i,j,k;
clrscr();
printf("Enter elements of 3x2 matrix A:");
for(i=0; i<3; i++)
{
for(j=0; j<2; j++)
{
}
}
printf("Enter elements of 2x3 matrix B:");
for(i=0; i<2; i++)
{
for(j=0; j<3; j++)
{
scanf("%d",&b[i][j]);
}
}
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
c[i][j]=0;
for(k=0; k<2; k++)
{
c[i][j] =c[i][j] + (a[i][k] * b[k][j]);
}

}
}
printf("Resultant Product Matrix :n");
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
printf("%3d",c[i][j]);
}
printf("n");
}
}
Output
Enter elements of 3x2 matrix A : 1 2 3 4 5 6
Enter elements of 2x3 matrix B : 1 2 3 4 5 6
Resultant Product Matrix :
9 12 15
19 26 33
29 40 51
/* Program to check whether given matrix is symmetric or not*/
void main()
{
int a[3][3],b[3][3],i,j,count=0;
clrscr();
printf("Enter elements of 3x3 matrix :");
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
}
}
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
b[i][j]=a[j][i];
}
}
printf("Transpose of matrix :n");
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
printf("%3d",b[i][j]);
}

printf("n");
}
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
if(a[i][j] == b[i][j])
count++;
}
}
if(count == 9)
printf("Symmetric Matrix");
else
printf("Non Symmetric Matrix");
}
Output
Enter elements of 3x3 matrix : 1 2 3 2 3 4 3 4 5
Transpose of matrix :
1 2 3
2 3 4
3 4 5
Symmetric Matrix

Multidimensional Arrays
Multidimensional arrays have three, four or more dimensions. The first dimension is called plane,
which consists of rows and columns. Arrays of four or more dimensions can be created and used, but
difficult to draw.
Three-dimensional array can be defined as array of two-dimensional arrays. In other words, it is
an array of arrays of array.
Declaration:
int a[2][3][4];
Here2 indicates a plane consisting of 3 rows and 4 columns
Initialization
int a[2][3][4] = {
{
{0,1,2,3},
{4,5,6,7},
{8,9,10,11}
},
{
{12,13,14,15},
{16,17,18,19},
{20,22,23,24}
}
};

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