C_Arrays.pptx

Editor: DEBASIS DWIBEDY
ARRAYS in C
Debasis Dwibedy
Assistant Professor*
Dept. CSE, VSSUT, Burla
*Personal Web Site: www.sites.google.com/view/debasis-dwibedy

What is an Array
An array is a fixed-size sequenced collection of related data items
of same type sharing a common name.
An array is a derived data type that holds a list of items of same
type.
Unlike the fundamental data types int, char, float, that holds only
one value, an array holds a list of values in contiguous memory
locations.
Example 1: int arr [10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; /* Array of first 10 natural numbers */
Example 2: float r [5] = {10.8, 9.6, 8.4, 11.5, 12.6}; /* Array of rate of interest of 5 banks */
Example 3: char name [8] = {‘D’, ‘E’, ‘B’, ‘A’, ‘S’, ‘I’, ‘S’, ‘0’} ; /* Array of characters*/

Types of Arrays
We can use arrays to represent not only simple lists of values but
also tables of data in two or three or more dimensions.
Accordingly, we have following types of arrays.
One –dimensional arrays
Two –dimensional arrays
Multi –dimensional arrays
A list of same type items can be given one variable name
using only one subscript, also known as the row-wise
representation of data. Eg: int arr [10] ;
A table of items can be given one variable name using two
subscripts, also known as the row and column wise
representation of data. Eg: int arr [3][3] ;
C allows arrays of three or more dimensions. The exact
limit is determined by the compiler. Eg: int arr [3][5][12] ;

One-Dimensional Arrays

Variable vs. Array
Variable Array
Declaration
data_type variable_name;
Eg. int mark ;
Memory Representation
mark
Declaration
data_type array_name [size] ;
Eg. int mark [5] ;
Memory Representation (column-measure order)
0
1
2
3
4
mark
mark[0]
mark[1]
mark[2]
mark[3]
mark[4]
1000
1002
1004
1006
1008
Real Memory Addresses
Base Address
Values at
Addresses
Array Name

Why to use an Array Type
Let’s consider that we need to store and print
a list of 1000 students' marks of an integer
type.
int main(void)
{
/* How long is the declaration and how many variables
used */
int studMark1, studMark2, studMark3, studMark4, …,
…, studMark998, stuMark999, studMark1000;
…
…
return 0;
}
We have to use 1000 variables of integer type to store and
print the marks. (that many variables are hard to remember)

Initialization of an Array
Method 1
/* Declaration*/
int mark[5];
/*Initialization*/
mark[0]=40;
mark[1]=45;
mark[2]=50;
mark[3]=35;
mark[4]=42;
Method 2
/* Declaration and
initialization*/
int mark[5]={40,45,50,35,42};
Method 3
/* Declaration and
initialization*/
int mark []={40,45,50,35,42} ;
Method 4
/* Declaration */
int mark [5], i ;
/* Initialization */
printf (“Enter 5 marks”) ;
for (i = 0 ; i < 5 ; i++)
{
scanf(“%d”, &mark[i]) ;
}
Not recommendable to omit
the size of the array, while
declaration and initialization
take place at the same time.

Character Array and String
/* Declaration and initialization*/
char name[9]={‘w’, ‘E’, ‘L’, ‘ ’, ‘C’, ‘O’, ‘M’, ‘E’, ‘0’};
‘W’
‘E’
‘L’
‘ ’
‘C’
‘O’
‘M’
‘E’
‘0’
0
1
2
3
4
5
6
7
8
/* Declaration and initialization*/
char name[9]={“WEL COME”};
Rule: The size of a character
array must be one more than
the number of characters to
be stored in memory or to be
displayed on the console. The
extra space is required to
store the “o” character to tell
the compiler explicitly about
the end of the array.

Array Initialization Tips
Error 1
/* Initializers are more than the
declared size*/
int mark[3]={40,45,50,35,42};
If we have more initializers, than the
declared size of the array, then the
compiler generates an error.
No Error
/* Initializers are less than the
declared size*/
int mark[5]={40,45,50};
If we have less initializers, than the
declared size of the array, then the
compiler does not generate an error
and allocates 0s to the vacant
locations of the integer array and ‘0’
to the character array.
No Error
/* Any reference to the array
outside the declared limit*/
int mark[5]={40,45,50, 35, 42};
printf(“%d”, mark[6]);
It would not cause an error, it outputs
a garbage value.

Run-Time Initialization of Array
Any array can also be initialized at run time explicitly. This
approach is useful for large arrays.
Example
/* Declaration */
int mark[100], i ;
for(i=0; i<100; i++)
{
if (i < 50)
mark[i]=45;
else
mark[i]=90;
}

Skeleton of a Program
Basic structure of a program that uses arrays.
#include<stdio.h>
void main()
{
/* Declaration of array and variables */
Declaration statements;
/* Initialization of array and variables */
Initialization statements;
/* Program Logic */
Logic statements;
/* Print the result */
Using for loops to print the array elements;
}

Program-1
W.A.P to display the sum of squares of any 10 real numbers.
#include<stdio.h>
void main()
{
/* Declaration */
int i ;
float arr[10], value, total=0.0 ;
/* Initialization of the Array*/
printf(“Enter values to the array”);
for(i = 0; i < 10; i++)
{
scanf(“%f”, &value);
arr[i] = value;
}
/* Print the Result*/
printf(“n total = %f”, total);
}
/* Computation of Total*/
for(i = 0; i < 10; i++)
{
total = total + arr[i] * arr[i];
}

Program-2
W.A.P that interchanges the odd and even positioned elements of an
array.
#include<stdio.h>
void main()
{
/* Logic*/
for (i = 0 ; i < n ; i = i+2)
{
t = num [i] ;
num [i] = num [i+1] ;
num [i+1] = t ;
}
/ * Print the Resultant Array * /
for ( i = 0 ; i < n ; i++ )
{
printf( “ %d”, num [i] ) ;
}
return 0 ;
}
/* Declaration */
int num[], i, n, t ;
/* Initialization of the Array*/
printf (“Enter size of the arrayn”) ;
scanf(“%d”, &n) ;
printf(“Enter elementsn”);
for(i = 0 ; i < n ; i++)
{
scanf(“%d”, &num[i]) ;
}

Program-3
Enter 5 students marks and display the percentage obtained by
each student as output.
#include<stdio.h>
void main()
{
/* Declaration */
int std[5], m1, m2, m3, m4, m5, i ;
/* Logic */
for(i=0; i<5; i++)
{
printf(“Enter marks of 5 subjects
of student %d”, i);
scanf(“%d%d%d%d%d”, &m1,
&m2, &m3, &m4, &m5);
std[i]=(m1+m2+m3+m4+m5)/5;
}
/* Print Results*/
for(i=0; i<5; i++)
{
printf(“%d”, std[i]);
}
}

Program-4
Enter 5 students marks into an array and sort the marks in an
ascending order.
Logic Execution of Iteration 1
for(i = 0 ; i < 5 ; i++)
{
j = i ;
for (k = i+1 ; k < 5 ; k++)
{
if (std [k] < std [i])
{
j = k ;
/* Swap the values of std [i] and std [j] */
temp = std [i] ;
std [i] = std [j] ;
std [j] = temp;
}
}
40 35 50 20 10
i, j k
40 35 50 20 10
k, j
i
35 40 50 20 10
i j k
35 40 50 20 10
i j k
35 40 50 20 10
k, j
i

Execution Continues
20 40 50 35 10
i j k
20 40 50 35 10
k, j
i
10 40 50 35 20
i j k
10 40 50 35 20
i j k
Termination of Iteration- 1 of outer For loop
Execution of Iteration 2
10 40 50 35 20
i, j k

Program-4 (Code)
Enter 5 students marks into an array and sort the marks in an
ascending order.
#include<stdio.h>
void main()
{
/* Declaration */
int std [5] = {40, 35, 50, 20, 10} ;
int i, j, k, temp ;
/* Logic */
for(i = 0 ; i < 5 ; i++)
{
j = i ;
for (k = i+1 ; k < 5 ; k++)
{
if (std [k] < std [i])
{
j = k ;
temp = std [i] ;
std [i] = std [j] ;
std [j] = temp;
}
}
/* Print the sorted Array*/
for(i = 0 ; i < 5 ; i++)
{
printf(“%dn”, std[i]);
}
}

Program-5
Given an array of n integers. W.A.P to find whether a number is
present in the array, if present, then print its position in the array.
#include<stdio.h>
int main()
{
/* Declaration */
int arr [], n, i, key ;
/* To know size of the Array */
printf(“Enter the number of
elements in the arrayn”) ;
scanf(“%d”, &n);
/* Initialization of the Array */
printf(“Enter %d numbersn”, n) ;
for (i = 0 ; i < n ; i++)
scanf(“%d”, &arr[i]);
/* Search Logic */
printf(“Enter the number to searchn”);
scanf(“%d”, &key);
for (i = 0 ; i < n ; i++ )
{
if (arr [i] = = key)
{
printf(“%d is present at position
%d n”, key, i+1);
break; } }
if (i = = n) {
printf (“%d is not present in the array”,
key);
return 0;
}

Program-6
W.A.P to copy the contents of one array of size 5 into another in the
reverse order.
#include<stdio.h>
void main()
{
/* Logic*/
for (i = 0, j = 4 ; i < 5 ; i++, j--)
{
arr2 [j] = arr1 [i] ;
}
/ * Print the Resultant Array * /
for ( i = 0 ; i < 5 ; i++ )
{
printf( “ n%d”, arr2 [i] ) ;
}
return 0 ;
}
/* Declaration */
int arr1[5], arr2 [5], i, j ;
/* Initialization of the Array 1*/
printf(“Enter 5 elements into array
n”);
for(i = 0 ; i < 5 ; i++)
{
scanf(“%d”, &arr1[i]) ;
}

Assignments
1. W.A.P to find the smallest and largest number in an array of n integers.
2. W.A.P to sort an array of n positive integers in descending order.
3. W.A.P to find the occurance of 1, 2, 3 in an array of following items
1, 2, 2, 3, 3, 2, 2, 1, 2, 1, 1, 1, 3, 2, 3, 3, 1, 2, 3, 1, 2, 3, 1.
4. W.A.P to find the mean and standard deviation of an array of n positive
integers.
5. Given are two one-dimensional arrays A and B which are sorted in
ascending order. W. A. P. to merge them into a single sorted array C that
contains every items from array A and B in ascending order.
6. Given an array of n positive integers. W.A.P to reverse the array elements.

Two-Dimensional Arrays

Definition
A 2-dimensional array represents a table of data in rows and columns
A table of items can be given one variable name using two subscripts
Eg: int m [5][5] ;
A 2-dimensional array is also called a matrix.
A 2-dimensional array is an amalgamation of several 1-D arrays.

Why to use a 2-D Array
Let’s consider that we need to store and print
the marks of 5 students in 5 subjects.
int main(void)
{
/* How long is the declaration and how many arrays are
used */
int std_1[5], std_2[5], std_3[5], std_4[5], std_5[5];
…
…
return 0;
}
We have to use 5 one-dimensional arrays of integer type with
5 rows to store 5 subjects marks of each students. (that many
arrays are hard to remember and maintain for a large program)

Why to use a 2-D Array
Can a single array be used to store and
display the marks of all 5 students ?
Yes, by a 2-D Array
Advantages
1. Number of 1-D array declarations can be reduced significantly.
2. It is convenient to remember and maintain a minimum number
of arrays.

Declaration
/* Declaration */
data_type array_name [row_size][column_size];
/* Example*/
int m [3][5] ; /* the compiler allocates 30 Bytes in contiguous memory locations */
Row 0
Row 1
Row 2
m[0][0] m[0][1] m[0][2] m[0][3] m[0][4]
m[1][0] m[1][1] m[1][2] m[1][3] m[1][4]
m[2][0] m[2][1] m[2][2] m[2][3] m[2][4]
0
1
2
0 1 2 3 4
Logical Representation of a 2-D Array
Accessing a 2-D array element by: array_name [row i][column j]
/* Example*/
printf ( “%d”, m [1][4] ) ; /* it will print value at location 2nd row and 5th column
Tabular
Form

Memory Layout
Lets consider the following 2-D array
Eg: int m [3][3] ;
How a 2-dimensional array is stored in the memory?
m[0][0] m[0][1] m[0][2] m[1][0] m[1][1] m[1][2] m[2][0] m[2][1] m[2][2]
Row 0 Row 1 Row 2
1000 1002 1004 1006 1008 1010 1012 1014 1016
Row-measure Representation of 2-D Array in Memory
printf(“The size of the array is %d Bytes”, sizeof(m)); /* The size of the array is 18 Bytes */
printf(“%u%u%u”, m+0, m+1, m+2)); /* 1000 1006 1012 */

Initialization
Method 1
/* Declaration*/
int m [2][2];
/*Initialization*/
m[0][0] = 40 ;
m[0][1] = 45 ;
m[1][0] = 50 ;
m[1][1] = 35 ;
Method 2
/* Declaration and
initialization*/
int m[2][2] = {
{40,45}, {50,35}
} ;
Method 3
/* Declaration and
initialization*/
int m[][2] = {
40, 45, 50, 35
} ;
Method 4
/* Declaration */
int m[2][2], i, j ;
printf (“Enter marks”) ;
for (i = 0 ; i < 2 ; i++)
{
for (j = 0 ; j < 2 ; j++)
scanf(“%d”, &m[i][j] );
}
Row size is optional, braces for
individual row is also optional,
but column size is compulsory
in the declaration and
initialization of a 2-D array.

Program-1
W.A.P to store and display 3 student marks of 3 different subjects.
#include<stdio.h>
void main()
{
/* Declaration */
int m[3][3], i, j ;
/* Store marks into m[3][3]*/
printf(“Enter marks of 3 studentsn”);
for(i = 0; i < 3; i++)
{
for (j = 0 ; j < 3 ; j++)
scanf(“%d”, &m[i][j]) ;
}
/* To know the size of the declared
m[3][3] */
printf (“%u”, sizeof(m) ) ;
/* Display the marks*/
for(i = 0 ; i < 3 ; i++)
{
for (j = 0 ; j < 3 ; j++)
{
printf(“%dt”, m[i][j]) ;
}
printf(“n”);
}
}

Program-2
W.A.P to print the largest number in a 2-D array and its position.
#include<stdio.h>
void main()
{
/* Logic*/
big = a[0][0], r = 0, c = 0 ;
for (i = 0 ; i < row_size ; i++)
{
for (j = 0 ; j < column_size ; j++)
{
if ( a[i][j] > big)
{
big = a[i][j];
r = i, c = j ; }
} }
/ * Print the Result * /
printf(“Largest=%d”, big ) ;
printf(The position of %d is %d th row
and %d th column”, big, r+1, c+1) ;
}
/* Declaration */
int a[][], i, j, big, row_size, column_size, r, c ;
/* Initialization of the Array a[][] */
printf (“Enter row and column sizen”) ;
scanf(“%d%d”, &row_size,
&column_size) ;
for(i = 0 ; i < row_size ; i++)
{
scanf(“%d”, &a[i][j]) ;
}

Transpose of a Matrix
Input Matrix
1
2
3
4
5
6
3 x 2
Interchanging the rows and columns
Resultant Matrix
1 2 3
4 5 6
2 x 3
/* Logic and print the resultant matrix*/
for (i = 0 ; i < column_size ; i++)
{
for (j = 0 ; j < row_size ; j++)
{
printf ( “ %dt”, a [j][i] ) ;
}
printf ( “ n” ) ;
}

Program-3
W.A.P to print the transpose of a matrix.
#include<stdio.h>
void main()
{
/* Logic and print the output array*/
for (i = 0 ; i < column_size ; i++)
{
for (j = 0 ; j < row_size ; j++)
{
printf ( “ %dt”, a [j][i] ) ;
}
printf ( “ n” ) ;
}
/* Declaration of 2-D Array and variables */
int a[][], i, j, row_size, column_size ;
/* Initialize and print the input items */
printf (“Enter row and column sizen”) ;
scanf(“%d%d”, &row_size,
&column_size) ;
for(i = 0 ; i < row_size ; i++)
{
scanf(“%d”, &a[i][j]) ;
printf( “ %d”, a[i][j] ) ;

Multiplication of two Matrices
Matrix m1
1
2
3
4
5
6
3 x 2
Resultant Matrix m3
1 2 3
4 5 6
2 x 3
/* Logic of matrix Multiplication */
for (i = 0 ; i < 3 ; i++)
{
for (j = 0 ; j < 3 ; j++)
{
sum = 0 ;
for ( k = 0; k < 2 ; k++ )
sum = sum + m1[i][k] * m2[k][j] ;
m3 [i][j] = sum ;
} }
X
Matrix m2
17 22 27
22 29 36
27 36 45
3 x 3
m3[0][0] = ( m1[0][0]* m2[0][0] ) + ( m1[0][1] * m2[1][0])
m3[0][1] = ( m1[0][0]* m2[0][1] ) + ( m1[0][1] * m2[1][1])
m3[0][2] = ( m1[0][0]* m2[0][2] ) + ( m1[0][1] * m2[1][2])
m3[1][0] = ( m1[1][0]* m2[0][0] ) + ( m1[1][1] * m2[1][0])
m3[1][1] = ( m1[1][0]* m2[0][1] ) + ( m1[1][1] * m2[1][1])
m3[1][2] = ( m1[1][0]* m2[0][2] ) + ( m1[1][1] * m2[1][2])
m3[2][0] = ( m1[2][0]* m2[0][0] ) + ( m1[2][1] * m2[1][0])
m3[2][1] = ( m1[2][0]* m2[0][1] ) + ( m1[2][1] * m2[1][1])
m3[2][2] = ( m1[2[0]* m2[0][2] ) + ( m1[2][1] * m2[1][2])
m X n n X p
m X p
i < m
j < p k < n

Program-4
W.A.P to show the multiplication of two 3 X 3 matrices.
#include<stdio.h>
void main()
{
/* Declaration of Arrays and variables */
int m1[3][3], m2[3][3], m3[3][3], i, j, k, sum;
/* Initialize and print items of m1 */
for(i = 0 ; i < 3 ; i++)
{
for (j = 0 ; j < 3 ; j++)
{
scanf(“%d”, &m1[i][j]) ;
printf( “ %dt”, m1[i][j] ) ;
}
printf (“ n”);
}
/* Initialize and print items of m2 */
for(i = 0 ; i < 3 ; i++)
{
for (j = 0 ; j < 3 ; j++)
{
scanf(“%d”, &m2[i][j]) ;
printf( “ %dt”, m2[i][j] ) ;
}
printf (“ n”);
}

Program-4 (contd..)
/* Print new matrx m3 containing the
product*/
printf(“The product of matrix m1 and
m2 is: n”) ;
for(i = 0 ; i < 3 ; i++)
{
for (j = 0 ; j < 3 ; j++)
{
printf( “ %dt”, m3[i][j] ) ;
}
printf (“ n”);
}
}
/* Logic of matrix Multiplication */
for (i = 0 ; i < 3 ; i++)
{
for (j = 0 ; j < 3 ; j++)
{
sum = 0 ;
for ( k = 0; k < 3 ; k++ )
{
sum = sum + m1[i][k] * m2[k][j] ;
}
m3 [i][j] = sum ;
}
}

Assignments
1. W.A.P to find the smallest and largest number in a n X n 2-D array.
2. W.A.P to find the 2nd smallest and 2nd largest number in a 3 X3 2-D array.
3. W.A.P to show the inverse of a 3 X 3 matrix.
4. W.A.P to show the multiplication of a m X n matrix with a n X P matrix.
5. A 6 X 6 matrix is entered through the key board. W.A.P to obtain the
determinant of this matrix.
6. W.A.P to add two 5 X 5 matrices and print the sum of elements of the
resultant matrix.
7. A 3 X 3 matrix is entered through key board. W.A.P to check whether
the input matrix is symmetric.

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