ARRAYSDeclaration, Initialisation , Reading &

Writing of Arrays

• We have used the fundamental data types, char, int, float, double.

• These types are constrained by the fact that a variable of these types can store only one value at any given time

• In many applications, we need to handle large volumes of data

• To process such large amounts of data, we need a powerful data types that would facilitate efficient storing, accessing and manipulation of data items

INTRODUCTION

• C supports a derived data type known as array.• An array is a fixed-sized sequenced collection of

elements of the same data type thats shares a common name.

• The common name a is the array name and each individual data item is known as an element of the array.

• The elements of the array are stored in the subsequent memory locations starting from the memory location given by the array name.

INTRODUCTION

Array can be classified as two types are,

1. One-Dimensional Array2. Two-Dimensional or

multidimensional Array

Types of Array

One-Dimensional Array

◦ A one-dimensional array can be used to represent a list of data items. It is also known as a vector.

Two-Dimensional Array

◦ A two dimensional array can be used to represent a table of data items consisting of rows and columns. It is also known as a matrix

Cont.,

Declaration of Arrays Every array must be declared before use like

other variables. The declarations of one-dimensional and

multidimensional arrays differ slightly. Declaration of One-dimensional array:

where data_type refers to the data type of elements in the array.

It can be a primitive or derived data type.  name is an identifier which represents the array name.size is an integer expression representing the total number of elements in the array.

data_type name1[size1], name2[size2],…, namen[sizen];

Declaratiaon of One-dimensional Arrays

The base address of an array is the address of the zeroth element (starting element) of that array.

When an array is declared, the compiler allocates a base address and reserves enough space in memory for all the elements of the array.

In C, the array name represents this base address. For example, float x[5]; is the declaration of a one-

dimensional array. It defines a float array x of size 5 that represents a

block of 5 consecutive storage regions.

Each element in the array is referred to by the array variables x[0], x[1], x[2] ,x[3] and x[4] where 0,1,2,3 and 4 represent subscripts or indices of the array.

In general, x[i] refers to the ith element of the array. The array subscripts always start at zero in C and they

are integer expressions. Hence, x[0] refers to the starting element, x[1] refers

to the next element and x[4] refers to the last element. The declaration double list[10], array[15]; declares

two arrays, named list and array having 10 and 15 elements respectively of double precision data type.

Declaration of One-dimensional Arrays…

The elements of an array may be assigned with the values using initialisation instead of reading them by the I/O functions.

An array can be initialised in its declaration only. The list of initialisers (values) are enclosed in braces. The initialisers are separated by commas and they must be

constants or constant expressions. One-dimensional array can be initialised as given below.

int a[4]={3,5, -8, 10}; The values within the braces are scanned from left end and

assigned to a[0], a[1] and so on. A semicolon should be placed after the closing brace.

Initialisation of Arrays

“For “ loops used extensively for array processing

Example 1: write a program to read an array and print.

#include<stdio.h>void main()

{ int i,a[10]; for(i=0;i<10;i++)

scanf(“%d”,&a[i]); for(i=0;i<10;i++)Printf(“\n %d”,a[i]);

}

Example2: write a program to read integer number and copy it another array.

Example3: write a program to read 10 values and sum these 10 values and print.

Example4: write a program to read 10 values and store it in another array in reverse order.

Example5: Write a c program for swapping of two arrays.

#include<stdio.h>void main(){ int x[2],i; printf("\nEnter the inputs:"); for(i=0;i<2;i++)

scanf("%d",&x[i]); for(i=0;i<2;i++)

printf("\nThe value in x[%d] is %d",i,x[i]);}

OUTPUT:Enter the inputs:36

The value in x[0] is 3The value in x[1] is 6

EXAMPLE

/*Determines the length of a message */#include<stdio.h>main(){char ch;int len=0;printf(“Enter a message : ”);ch=getchar();while (ch!=‘\n’) {len++;ch=getchar();}printf(“Your message was %d character(s) long. \n”, len);return 0;}

CHARACTER ARRAY The c languages treats strings as arrays of characters The compiler terminates the character strings with an

additional null (‘\0’) character. String is a one dimensional array of characters in c. The element name[10] holds the null character ‘\0’ at

the end When declaring character arrays, we must always

allow one extra elements space for the null terminator

#include<stdio.h>

void main(){ int i=0;

char a[]="abcd";

while(a[i]!='\0') {

printf("\t%c",a[i]);i++;}

}

OUTPUT:a b c d

There are different way to initialize a character array variable.

char name[10]=“StudingTonight”; //valid initialization

char name[10]={‘L’,’E’,’S’,’S’,’O’,’N’,’S’,’\0’}; // valid Init

Some example for illegal Initialization of character array are,

char ch[3]=“hello”; // Illegal char str[4];

str=“hello”; //illegal

Declaring and Initialization of character array

Format:

data_type array_name[row_size1][column_size1]; The first subscript represents the row size and the second subscript

represents the column size. The value in the ith row and jth column is referred to by name[i][j]. The total number of elements in a two dimensional array is

calculated by multiplying the number of rows by the number of columns.

In two-dimensional arrays, the values are stored row by row.

Declaration of Two-dimensional Arrays

int x[3][2];

Example

For example, the declaration int a[3][2] ,b[7][4]; defines the two-dimensional integer arrays a and b.

These arrays are arrays of integer arrays. Six (rows * columns) elements of a are stored row by row in

the consecutive memory locations. This method of storing the elements in the memory is

known as row major order storage representation The zeroth element of array a is denoted by a[0][0] and the

last element in that array is denoted by a[2][1]. Similarly, for the array b, the zeroth element and the last

element are represented by b[0][0] and b[6][3] respectively.

Declaration of Two-dimensional Arrays…

Declaration of Two-dimensional Arrays…

Starting element a[0][0] a[0][1] a[1][0] a[1][1] a[2][0] Last element a[2][1]

Row 0

Row 1Row 1

Row 2

Storage representation of matrix a

Syntax:data_type array_name[row_size][col_size]={variables};

A two-dimensional array can be initialised as given below.int a[3][2] = {20, 25, -3, 8, -5, 7};

Here, the initialised values are assigned to the array elements according to the order of the storage in the memory.

But if the initialisers are enclosed within the inner braces as given below

int a[3][2] = {{20,25}, {-3, 8}, {-5,7}}; The initialised values within the inner braces are assigned to each row. To enforce the assignment of each row, it is essential to use the inner

braces.

Initialisation of Arrays

If the number of values initialised for an array is less than the size mentioned, the missing elements are assigned zero. In the initialisation

int a[3][4] = { {1,2},{4,8,15} };

the elements a[0][0] and a[0][1] of the zeroth row and a[1][0], a[1][1] and a[1][2] of the first row are initialised with the values 1,2,4,8 and 15 respectively.

All the other elements are initialised to zero.

If it is given as int a[3][4] = {1,2,3,8,15};

 the values are assigned from the left end to a[0][0], a[0][1], a[0][2], a[0][3], and a[[1][0] according to the order of the storage representation.

If the number of initialisers exceeds the size of the array, it is an error.

Initialisation of Arrays…

The size of a one-dimensional array need not be mentioned in its

initialisation.

In this case, the compiler will count the values assigned and take it as

the size of that array.

In multidimensional arrays the leftmost subscript may be omitted and

all the others must be specified. The initialisation 

int x[ ] = {2,4,6,8,10};

makes the array x having 5 elements

float a[ ][2] = {{3.2,4.8}, {5.3,3.7}};

makes the array a having 2 rows and 2 columns.

Initialisation of Arrays…

EXAMPLE#include<stdio.h>void main(){ int i,j; int x[2][2]={ {1,50},

{2,75}};

for(i=0;i<2;i++)for(j=0;j<2;j++)

printf("\nThe value in x[%d][%d] is %d",i,j,x[i][j]);

}

OUTPUT:The value in x[0][0] is 1

The value in x[0][1] is 50The value in x[1][0] is 2The value in x[1][1] is 75

EXAMPLE#include<stdio.h>void main(){ int i,j; int x[][2]={ {1,50},{2,75},{3,65}};

for(i=0;i<=2;i++)for(j=0;j<2;j++)

printf("\nThe value in x[%d][%d] is %d",i,j,x[i][j]);

}

OUTPUT:The value in x[0][0] is 1The value in x[0][1] is 50The value in x[1][0] is 2The value in x[1][1] is 75The value in x[2][0] is 3The value in x[2][1] is 65

/* PROGRAM TO FIND THE MINIMUM VALUE AND ITS POSITION */ #include<stdio.h> #define MAX 5 main( ) { int a[MAX],i,min; int pos = 0; /* Fixing position if the first number is the minimum value */ printf("Enter the array elements\n"); for(i=0;i<MAX;i++) scanf("%d",&a[i]); min=a[0]; for(i=1;i<MAX;i++) if(a[i] < min) { min=a[i]; pos=i; /* Fixing the minimum value position*/ } printf(“ MINIMUM VALUE = %d\n”,min); printf(“ POSITION = %d\n”,pos); }

SAMPLE INPUT AND OUTPUT Enter the array elements14 29 37 25 45 MINIMUM VALUE = 14POSITION = 0

#define MAXROW 2#define MAXCOL 4main( ) { int s[MAXROW][MAXCOL],t[MAXCOL][MAXROW]; int i,j; printf("Enter the values of the matrix\n"); for(i=0;i<MAXROW;i++) for(j=0;j<MAXCOL;j++) scanf("%d",&s[i][j]); printf("\nGiven Matrix\n\n"); for(i=0;i<MAXROW;i++) { for(j=0;j<MAXCOL;j++) printf("%d\t",s[i][j]); printf("\n"); }

/* PROGRAM TO FIND THE TRANSPOSE OF A MATRIX */

for(i=0;i<MAXCOL;i++) for(j=0;j<MAXROW;j++) t[i][j] = s[j][i]; printf("\nTranspose of the matrix\n\n"); for(i=0;i<MAXCOL;i++) { for(j=0;j<MAXROW;j++) printf("%d\t",t[i][j]); printf("\n"); }}

SAMPLE INPUT AND OUTPUT Enter the values of the matrix10 20 30 40 50 60 70 80 

Given Matrix 10 20 30 4050 60 70 80 Transpose of the matrix 10 5020 6030 7040 80

#include<stdio.h>#include<conio.h>void main(){ int i,j,k,r1,r2,c1,c2; int a[5][5],b[5][5],c[5][5]; clrscr(); //step1: printf("\n Enter the size of

matrix A:"); scanf("%d%d",&r1,&c1); printf("\n Enter the size of

matrix B: "); scanf("%d%d",&r2,&c2); if((c1==c2)&&(r1==r2))

goto step2; else

goto step1;

//step2: printf("\n Enter the elements of matrix A \n"); for(i=0;i<r1;i++) {

for(j=0;j<c1;j++){

scanf("%d",&a[i][j]);}

} printf("\n Enter the elements of matrix B \n"); for(i=0;i<r2;i++) {

for(j=0;j<c2;j++){

scanf("\t%d",&b[i][j]);}

}

for(i=0;i<r1;i++) {

for(j=0;j<c1;j++){c[i][j]=0; c[i][j]=c[i][j]+a[i][j]+b[i][j];}

} printf("\n The resultant

matrix after addition of A & B is\n");

for(i=0;i<r1;i++) {

for(j=0;j<c1;j++)printf("%d\t",c[i][j]);printf("\n");

} getch();}

OUTPUT:Enter the size of matrix A: 22 Enter the size of matrix B: 22 Enter the elements of matrix

A2222 Enter the elements of matrix

B3333 The resultant matrix after

addition of A&B is5 55 5

/* PROGRAM TO REMOVE THE DUPLICATE ELEMENTS IN AN ARRAY */ #define MAX 5main( ) { int a[MAX]; int i,j,k,n=MAX,p; for(i=0;i<n;i++) { printf("Enter the value of a[%d]:\n",i); scanf("%d",&a[i]); } printf("Array before deleting duplicate elements\n"); for(i=0;i<n;i++) printf("%d\t",a[i]); for(i=0;i<n;i++) { for(j=i+1;j<n;j++)

{ if(a[i] == a[j]) { p = i ; for(k=j;k<n;k++) a[k] =a[++j]; j = p; n--; } } } putchar('\n'); printf("Array after deleting duplicate elements\n"); for(i=0;i<n;i++) printf("%d\t",a[i]); putchar('\n'); } 

 SAMPLE INPUT AND OUTPUT Enter the value of a[0]:5Enter the value of a[1]:8Enter the value of a[2]:5Enter the value of a[3]:12Enter the value of a[4]:8Array before deleting duplicate elements5 8 5 12

8Array after deleting duplicate elements5 8 12

Example Programs

Example program 2/* PROGRAM TO SORT AN ARRAY */ #define MAX 5main( ) { int a[MAX],i,j,temp; printf("Enter the array elements\n"); for(i=0;i<MAX;i++) scanf("%d",&a[i]); for(i=0;i<MAX;i++) for(j=i+1;j<MAX;j++) { if(a[i] >a[j])

Example Programs

Example program 2… { temp = a[i]; a[i] = a[j]; a[j] = temp; } } printf("\nAscending order\n"); for(i=0;i<MAX;i++) printf("%d\t",a[i]); printf("\nDescending order\n"); for(i=MAX-1;i>=0;i--) printf("%d\t",a[i]); }

SAMPLE INPUT AND OUTPUT Enter the array elements11 15 20 45 15Ascending order11 15 15 20 45Descending order45 20 15 15 11

Example Programs

Example program 3 /*PROGRAM TO CONVERT A 2-D ARRAY TO 1-D ARRAY */ #define MAXROW 3#define MAXCOL 2main( ) { int a[MAXROW][MAXCOL],b[MAXROW*MAXCOL]; int i,j,k=0; printf("Enter the matrix elements in row order\n"); for(i=0;i<MAXROW;i++) for(j=0;j<MAXCOL;j++) { scanf("%d",&a[i][j]);

Example Programs

Example program 3… b[k++] = a[i][j]; } printf("Given two-dimensional array\n"); for(i=0;i<MAXROW;i++) { for(j=0;j<MAXCOL;j++) printf("%d\t",a[i][j]); printf("\n"); } printf("Equivalent one-dimensional array\n"); for(i=0;i<MAXROW*MAXCOL;i++) printf("%d\t",b[i]); }

SAMPLE INPUT AND OUTPUT Enter the matrix elements in row order10 15 20 25 30 35Given two-dimensional array10 1520 2530 35Equivalent one-dimensional array10 15 20 25 30 35