Array and its operation in C programming

Introduction to Arrays
 An array is used to process a collection of data of the
same type
 Examples: A list of names
A list of temperatures
 Why do we need arrays?
 Imagine keeping track of 100 test scores or 1000 in
memory
 How would you name all the variables?
 How would you process each of the variables?
Array in C 2
Prepared by : Er. Rhishav Poudyal

 An array is a collection of elements of the same type
that are referenced by a common name.
 Compared to the basic data type (int, float & char) it
is an aggregate or derived data type.
 All the elements of an array occupy a set of contiguous
memory locations.
 Consider the following issue:
"We have a list of 1000 students' marks of an integer
type. If using the basic data type (int), we will declare
something like the following…"
int studMark0, studMark1, studMark2, ..., studMark999;

 Can you imagine how long we have to write the
declaration part by using normal variable
declaration?
int main(void)
{
int studMark1, studMark2, studMark3,
studMark4, …, …, studMark998,
stuMark999, studMark1000;
…
…
return 0;
}

Definition and Initialization
 Array is defined as the user defined (derived) data type
which hold multiple data having same kind of data
type.
 An array is defined using a declaration statement.
data_type array_name[size];
 allocates memory for size elements
 subscript of first element is 0
 subscript of last element is size-1
 size must be a constant
5
Array in C Prepared by : Er. Rhishav Poudyal

Definition – Array
 A collection of objects of the same type stored
contiguously in memory under one name
 May be type of any kind of variable
 May even be collection of arrays!
 For ease of access to any member of array
 For passing to functions as a group
6

Initializing Arrays
 To initialize an array when it is declared
 The values for the indexed variables are enclosed in
braces and separated by commas
 Example: int children[3] = { 2, 12, 1 };
Is equivalent to:
int children[3];
children[0] = 2;
children[1] = 12;
children[2] = 1;
Array in C 7

One-Dimensional Arrays
 Suppose, you need to store years of 100 cars. Will you
define 100 variables?
int y1, y2,…, y100;
 An array is an indexed data structure to represent several
variables having the same data type: int y[100];
8
y[0] y[1] y[2] … y[k-1] y[k] y[k+1] … y[98] y[99]

Arrays
 Array
 Group of consecutive memory locations
 Same name and type
 To refer to an element, specify
 Array name
 Position number
 Format:
arrayname[ position number ]
 First element at position 0
 n element array named c:
 c[ 0 ], c[ 1 ]...c[ n – 1 ]
9

One-Dimensional Arrays (cont’d)
 An element of an array is accessed using the array name
and an index or subscript, for example: y[5] which can be
used like a variable
 In C, the subscripts always start with 0 and increment by 1,
so y[5] is the sixth element
 The name of the array is the address of the first element
and the subscript is the offset
10
y[0] y[1] y[2] … y[k-1] y[k] y[k+1] … y[98] y[99]

Arrays
 Array elements are like normal variables
c[ 0 ] = 3;
printf( "%d", c[ 0 ] );
 Perform operations in subscript. If x equals 3
c[ 5 - 2 ] == c[ 3 ] == c[ x ]
11

Declaring Arrays
 When declaring arrays, specify
 Name
 Type of array
 Number of elements
arrayType arrayName[ numberOfElements ];
 Examples:
int c[ 10 ];
float myArray[ 3284 ];
 Declaring multiple arrays of same type
 Format similar to regular variables
 Example:
int b[ 100 ], x[ 27 ];
12

Examples (continued)
 int C[]
 An array of an unknown number of integers (allowable in a
parameter of a function)
 C[0], C[1], …, C[max-1]
 int D[10][20]
 An array of ten rows, each of which is an array of twenty
integers
 D[0][0], D[0][1], …, D[1][0], D[1][1], …, D[9][19]
 Not used so often as arrays of pointers
13

Examples (continued)
 Initializers
int n[ 5 ] = { 1, 2, 3, 4, 5 };
 If not enough initializers, rightmost elements become 0
int n[ 5 ] = { 0 }
 All elements 0
 If too many a syntax error is produced syntax error
 C arrays have no bounds checking
 If size omitted, initializers determine it
int n[ ] = { 1, 2, 3, 4, 5 };
 5 initializers, therefore 5 element array
14

Declaring an Array
 An array, named score, containing five variables of
type int can be declared as
int score[ 5 ];
 This is like declaring 5 variables of type int:
score[0], score[1], … , score[4]
 The value in brackets is called
 A subscript
 An index
Array in C 15

Assigning values to an array
16
For loops are often used to assign values to an array
Example:
int list[5], i;
for(i=0; i<5; i++){
list[i] = i;
} list[0]
list[3]
list[4]
list[1]
list[2]
0
1
2
3
4
list[0]
list[1]
list[2]
list[3]
list[4]
OR
for(i=0; i<=4; i++){
list[i] = i;
}

Assigning values to an array
17
Give a for loop to assign the below values to list
int list[5], i;
for(i=0; i<5; i++){
list[i] = 4-i;
}
list[0]
list[3]
list[4]
list[1]
list[2]
4
3
2
1
0

Array Element
 May be used wherever a variable of the same type may
be used
 In an expression (including arguments)
 On left side of assignment
 Examples:–
A[3] = x + y;
x = y – A[3];
z = sin(A[i]) + cos(B[j]);
18

Array Elements (continued)
 Generic form:–
 ArrayName[integer-expression]
 ArrayName[integer-expression] [integer-expression]
 Same type as the underlying type of the array
 Definition:– Array Index – the expression between the
square brackets
19

Array Elements (continued)
 Array elements are commonly used in loops
 E.g.,
for(i=0; i < max; i++)
A[i] = i*i;
sum = 0;
for(j=0; j < max; j++)
sum += B[j];
20

Array Initialization
 int A[5] = {2, 4, 8, 16, 32};
 Static or automatic
 int B[20] = {2, 4, 8, 16, 32};
 Unspecified elements are guaranteed to be zero
 int C[4] = {2, 4, 8, 16, 32};
 Error — compiler detects too many initial values
 int D[5] = {2*n, 4*n, 8*n, 16*n,
32*n};
 Automatically only; array initialized to expressions
21

Implicit Array Size Determination
 int days[] = {31, 28, 31, 30, 31,
30, 31, 31, 30, 31, 30, 31};
 Array is created with as many elements as initial values
 In this case, 12 elements
 Values must be compile-time constants (for static
arrays)
 Values may be run-time expressions (for automatic
arrays)
22

Caution! Caution! Caution!
 It is the programmer’s responsibility to avoid indexing
off the end of an array
 Likely to corrupt data
 May cause a segmentation fault
 Could expose system to a security hole!
 C does NOT check array bounds
 I.e., whether index points to an element within the array
 Might be high (beyond the end) or negative (before the array
starts)
23

Initializing Arrays
 Arrays can be initialized at the time they are declared.
Examples:
double taxrate[3] ={0.15, 0.25, 0.3};
char list[5] = {‘h’, ’e’, ’l’, ’l’, ’o’};
double vector[100] = {0.0};
/* assigns zero to all 100 elements */
int s[] = {5,0,-5}; /*the size of s is 3*/
24

Find Maximum
 Find maximum value in data array
int data[100], max, i;
for (i=0; i<100; i++)
scanf(“%d”,&data[i]);
max = data[0];
for (i=1; i<100; i++){
if (data[i] > max)
max = data[i];
}
printf("Max = %dn",max);
26

Find average
27
 Find average of values in data array
int data[100], sum, i, avg;
for (i=0; i<100; i++)
data[i] = rand_int(10,109);
sum = 0;
for (i=0; i<100; i++)
{
sum = sum + data[i];
}
avg = (double)sum/100;
printf(“Avg = %lfn", avg);

Number of elements greater than
average
 After finding the average as shown in previous slide,
use the following code
28
count = 0;
for (i=0; i<100; i++)
{
if (data[i] > avg)
count++;
}
printf(“%d elements are greater than
avg”, count);

Copy array1 to array2 in reverse
order
29
6 3 1 9 7 2
0 2
1 3 4 5
2 7 9 1 3 6
array1
array2

What are Multidimensional
Arrays
 A multidimensional array is treated as an array of
arrays.
 Let a be a k-dimensional array; the elements of a
can be accessed using the following syntax:
a [ i1 ] [ i2 ]…[ ik ]
where i1, i2, ….., ik
Array in C 30

Multidimensional Arrays
 Applying what we learned about simple arrays to
multidimensional array, we get the following:
A k-dimensional array can be created with either of
the following methods:
 Using the new operator
 Using the k-dimensional initializer
Array in C 31

Creating k-dimensional Array
Using the new operator
new Type [ n1] [n2]…[nk]
 Size of each dimension is
n1, n2, …,nk, respectively.
 All the elements in the
array are initialized to
default initial values
based on the type of the
elements
 Using k-dimensional array
initializer
{I1, I2, ...., Ik}
 where each I1, I2, ...., Ik is a
(k-1)- dimensional array
initializer.
Array in C 32

Examples…
 Using the new operator, the
following example is of
creating and initializing a
two-dimensional array.
double mat1[4 ][5 ]
This creates a 4 x 5 two-
dimensional array. All
elements are initialized to
0.0.
 Using k-dimensional array initializer,
the following example is of creating
and initializing a two-dimensional
array.
int mat2[ ] [ ] = {{1, 2, 3}, {4, 5, 6}};
This creates a 2 x 3 two-dimensional
array. The elements are initialized as:
mat2[0][0]=1 mat2[1][0]= 4
mat2[0][1]=2 mat2[1][1]= 5
mat2[0][2]=3 mat2[1][2]= 6
Array in C 33

Two Dimensional Arrays
 A two dimensional array stores data as a
logical collection of rows and columns.
 Each element of a two-dimensional array has a row
position and a column position.
 To access an element in a two-dimensional array,
you must specify the name of the array followed
by:
 a row offset
 a column offset
Array in C 34

Declaration and Initialization
 The declaration of a two-dimensional array
requires a row size and a column size.
 All array elements must be of the same type.
 Elements accessed by two offsets – a row offset and
a column offset.
 The name of the array holds the address of the first
byte of memory
Array in C 35

Example
//Declaration
int data[2][3];
Memory Snapshot
?
?
?
?
?
?
data
Array in C 36

Example
//Declaration
int data[2][3];
? ? ?
? ? ?
row 0
row 1
col 0 col 1 col 2
row/column form:
Array in C 37

2D Array Definition Syntax
Syntax:
data_type identifier[ [row_size] ][column_size] [=
initialization_list ];
//row_size and column_size must be integer constants
Examples
int data[2][5]; //allocates consecutive memory
for 10 integer values
double t[2][2] = {{3.0,5.0},{2.1,7.2}};
//allocates and initializes
Array in C 38

Initialization Examples
int temp[4][3] = {50, 70, 60, 48, 75,
62, 51, 69, 60, 52, 78, 63};
int temp[4][3] = {{50, 70, 60}, {48, 75, 62},
{51, 69, 60}, {52, 78, 63}};
int temp[][3] = {{50, 70, 60}, {48, 75, 62},
{51, 69, 60}, {52, 78, 63}};
int temp[][3] = {50, 70, 60, 48, 75, 62, 51,
69, 60, 52, 78, 63};
Array in C 39

Example: Input
 Nested for loops are often used when
inputting and assigning values to a two-dimensional
array.
 Nested loops are generally useful for getting
around the 2D arrays…
//Declaration
double table[RSIZE][CSIZE];
for (int i=0; i<RSIZE; ++i) //every row
for (int j=0; j<CSIZE; ++j )//every col
scanf(“%lf”,&table[i][j];
Array in C 40

Example: Assignment
//Declaration
const int RSIZE(3),CSIZE(2);
double v[RSIZE][CSIZE];
for (int i=0; i<RSIZE; ++i) //every row
for (int j=0; j<CSIZE; ++j )//every col
v[i][j] = i+j;
0 1
1 2
2 3
V
Array in C 41

Example: Computations
 Compute the average value of an array
with n rows and m columns.
double sum(0), average;
for (int i=0; i<n; ++i)//every row
for (int j=0; j<m; ++j )//every col
sum += array[i][j];
average = sum / (n*m);
Array in C 42

Example: Computations
 Compute the average value of the nth row
of a 2D array with r rows and c columns.
double sum(0), rowAverage;
for (int j=0; j<c; ++j ) //every col
sum += array[n][j];
average = sum / c;
Array in C 43

Outputting 2D Arrays
 Two dimensional arrays are often printed in a row by
row format, using nested for statements.
 When printing the row values of an array, be sure to
print:
 whitespace between the values in a row.
 a newline character at the end of each row.
Array in C 44

Example: Printing
for (int i=0; i<n; ++i) {//every row
{ for (int j=0; j<m; ++j )//every col
printf(“%d”,array[i][j]);
}
Array in C 45

Matrix
 A matrix is a set of numbers arranged
in a rectangular grid with rows and columns.
 A square matrix has the same number of rows as
columns.
 Row and Column offsets in Matrices are 1-based.
 2D Arrays are useful for representing matrices.
Array in C 46

Matrix Computations and
Operations
 The determinant of a matrix is a scalar value used
in computing matrix inverses and solving systems of
simultaneous equations.
 The transpose of a matrix is a new matrix in which the rows
of the original matrix are the columns of the transpose.
 Matrices of the same size may be added or subtracted
element-by-element.
 Matrix multiplication (M * N) is defined only when the
number of columns of M is equal to the number of rows in
N.
 Result has the size rows(M) x cols(N)
Array in C 47

C program to store temperature of
two cities for a week and display it.
48

49
const int CITY = 2;
const int WEEK = 7;
void main()
{
int temperature[CITY][WEEK];
for (int i = 0; i < CITY; ++i) {
for(int j = 0; j < WEEK; ++j) {
printf("City %d, Day %d: ", i+1, j+1);
scanf("%d", &temperature[i][j]);
}
}
printf("nDisplaying values: nn");
for (int i = 0; i < CITY; ++i) {
for(int j = 0; j < WEEK; ++j)
{
printf("City %d, Day %d = %dn", i+1, j+1,
temperature[i][j]);
}
}
}

WAP to find the sum of two matrices
of order 2*2 .
50

51
#include <stdio.h>
int main()
{
float a[2][2], b[2][2], c[2][2];
int i, j;
printf("Enter elements of 1st matrixn");
for(i=0; i<2; ++i)
for(j=0; j<2; ++j)
{
printf("Enter a%d%d: ", i+1, j+1);
scanf("%f", &a[i][j]);
}
printf("Enter elements of 2nd matrixn");
for(i=0; i<2; ++i)
for(j=0; j<2; ++j)
{
printf("Enter b%d%d: ", i+1, j+1);
scanf("%f", &b[i][j]);
}

52
// adding corresponding elements of two arrays
for(i=0; i<2; ++i)
for(j=0; j<2; ++j)
{
c[i][j] = a[i][j] + b[i][j];
}
// Displaying the sum
printf("nSum Of Matrix:");
for(i=0; i<2; ++i)
for(j=0; j<2; ++j)
{
printf("%.1ft", c[i][j]);
if(j==1)
printf("n");
}
return 0;
}

WAP to Find Transpose of a Matrix
53

54
#include <stdio.h>
void main()
{
int a[10][10], transpose[10][10], row, col, i, j;
printf("Enter rows and columns of matrix: ");
scanf("%d %d", &row, &col);
printf("nEnter elements of matrix:n");
for(i=0; i<row; ++i)
for(j=0; j<col; ++j)
{
printf("Enter element a%d%d: ",i+1, j+1);
scanf("%d", &a[i][j]);
}

55
// Finding the transpose of matrix a
for(i=0; i<row; ++i)
for(j=0; j<col; ++j)
{
transpose[j][i] = a[i][j];
}
// Displaying the transpose of matrix a
printf("nTranspose of Matrix:n");
for(i=0; i<col; ++i)
for(j=0; j<row; ++j)
{
printf("%d ",transpose[i][j]);
if(j==r-1)
printf("nn");
}
}

Program to Multiply Two Matrices
56

57
#include <stdio.h>
int main()
{
int a[10][10], b[10][10], result[10][10], r1, c1, r2, c2, i, j, k;
printf("Enter rows and column for first matrix: ");
scanf("%d %d", &r1, &c1);
printf("Enter rows and column for second matrix: ");
scanf("%d %d",&r2, &c2);
// Column of first matrix should be equal to row of second
matrix and
if (c1 != r2)
{
printf("Error! column of first matrix not equal to row of
second.nn");
}

58
// elements of first matrix.
printf("nEnter elements of matrix 1:n");
for(i=0; i<r1; ++i)
for(j=0; j<c1; ++j)
{
printf("Enter elements a%d%d: ",i+1, j+1);
scanf("%d", &a[i][j]);
}
// elements of second matrix.
printf("nEnter elements of matrix 2:n");
for(i=0; i<r2; ++i)
for(j=0; j<c2; ++j)
{
printf("Enter elements b%d%d: ",i+1, j+1);
scanf("%d",&b[i][j]);
}

59
// Initializing all elements of result matrix to 0
for(i=0; i<r1; ++i)
for(j=0; j<c2; ++j)
{
result[i][j] = 0;
}
// Multiplying matrices a and b and
// storing result in result matrix
for(i=0; i<r1; ++i)
for(j=0; j<c2; ++j)
for(k=0; k<c1; ++k)
{
result[i][j]+=a[i][k]*b[k][j];
}

60
// Displaying the result
printf("nOutput Matrix:n");
for(i=0; i<r1; ++i)
for(j=0; j<c2; ++j)
{
printf("%d ", result[i][j]);
if(j == c2-1)
printf("nn");
}
return 0;
}

Array and its operation in C programming

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