ARRAY IN C

Learning objectives
At the end of this chapter, student should able to:
1. Define what is arrays
2. Determine an array declaration, accessing element of array, enter and read data
from an array from the source code
3. Initialize the arrays 1D, 2D or multi dimension array
4. Identify the relationship between pointer and array

Array
Arrays are a collection of similar variables of any basic type.

Array
Arrays are a collection of similar variables of any basic type.
They are declared as follows:
The declaration int numbers[50] means there are 50 integers
associated with the name numbers
They are individually named: numbers[0], numbers[1], numbers[2],....numbers[49]
Each array element can be used as any other variable of the same type.
eg. numbers[5] = 100 + counters[1]*2;
Variables or expressions can be used to specify the array index:
eg. numbers[abc] = numbers[fred+1];

Limitations and Dangers in the Use of an Array
Unlike some languages, such as Pascal, it is not possible to:
1. Assign whole arrays one to another.
eg. int fred[10], joe[10];
fred = joe; /*invalid statement*/
2. Compare one array with another.
eg. int fred[10], joe[10];
if (fred == joe) abc++; /*valid but always false*/

Strings
An array of characters with a null byte at the end is called a character "string". It can be printed directly using
%s in printf:
This will send to the standard output screen the message: Hello Joe!
Note:
Constant strings cannot be assigned to string arrays: eg. str = "Fred"; /*invalid */
Constant strings cannot be compared to string arrays: eg. if (str == "Joe") ...; /*valid, but always false*/

A simple program using strings in Array

A simple program using Arrayc

A simple program using Array
Array Declaration
• An array need to be
declared
• Int = type of variables,
• marks = name of
variable,
• [30] element of array /
dimension
Accessing element of array
All the array element are
numbered, starting 0.
Marks [2] = 3rd element
Entering data into an array
• for loop, repeating process
30 times.
• 1st element, marks[0] as I
has value 0 and will
repeated until i=29
Reading data from an array
• Reads the data and
calculate average
• For loop, students marks to
be added to a total stored,
sum and result will be
divided by 30

Initialization of Arrays
• Arrays can be initialized as follows:
int xyz[6]={4,7,3,9,100,6};
Too many initializers will cause a compilation error.
• Character arrays can also have a string initialization:
char name[12]="Fred Bloggs";
but it is important that the array is big enough for the given characters and the null byte
terminator.
• If an array is initialized the size can be left to default to the number of initializing values.
char greeting[]="Hello!";
int abc[]={1,2,3,4,5,6,7};
Both these arrays would default to a size of 7 elements.

#include <stdio.h>
#define N 5
int main ( )
{
int i;
float a [N] = (2.0, -15.0, 12.0, -5.4, 1.9);
float sum = 0.0;
for (i=0; i < N; i++) sum = sum + a [i] ;
printf (“The sum is = %f.n”, sum);
return 0;
}
The output is : The sum is = -4.500000
A simple program using initialization of Array

Two dimensional arrays
The 2D array is also called a matrix. To declare 2D integer array of size x, y –
data_type array_Name [x] [y];
Int 2D_array [10] [20];
What is the size of 2D array?
The total number of elements that can be stored in a multidimensional array can be
calculated by multiplying the size of all dimensions.
Type array_Name [x] [y];  (x*y)
Int 2D_array [10] [20];  (10 * 20)  200

A 2D array can be thought as a table, which will have x number of rows and y number of
columns. A 2D array which contains 3 rows and 4 columns can be shown as below-
Thus, every element in array a is identified by an element name of form a [i] [j]
Two dimensional arrays

2D arrays : Initialization
2D arrays may be initialized by specifying bracketed values for each row.
 Following is an array with 3 rows and 4 columns
int 2D_array [3] [4] = {
{0,1,2,3}; //initializers for rows index 0
{2,3,4,5}; //initializers for rows index 1
{4,5,6,7}; //initializers for rows index 2
 Nested braces which indicated the intended row are optional-
int a [3] [4] = {0,1,2,3,4,5,6,7,8,9,10,11};

A program to input elements in 2D arrays

Output result

2D arrays: Storage Allocation
Array declaration : int a [3] [4]
Array elements:

2D arrays: Storage Allocation

A program add to matrix in 2D arrays
#include <stdio.h>
#include <conio.h>
void main ()
{
int a [3][3], b[3] [3], c[3][3];
int i,j;
printf("enter the elements in both array:");
for (i=0; i<3; i++)
{
for (j=0; j<3; j++)
{
scanf("%d", &a[i][j]);
}
}
for ( i = 0; i < 3; 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]= a[i][j] + b[i][j];
printf("%d",c[i][j]);
}
printf("n");
}
getch();
}

Output result

2D arrays: Accessing elements
An element in 2D array is accessed by using the subscripts / array indices
 Row index and column index of array: int val = a [2] [3]
8 16 9 52
3 15 27 6
14 25 2 10

Multi-dimensional arrays
Arrays can be nested, i.e., they can take more than 1 indices. Nested arrays
(multidimensional arrays) can represent matrices in linear algebra. For example, the
components of a 2 × 5 matrix, a, can be represented in C as

Initialising Multi Dimensional Arrays
Multi dimensional arrays can be initialized as a single list of initializer values:
int x [3] [4] = {3,2,10,5,6,2};
int y [3] [4] [2] = { {2,4}, {7,8}, {3,4}, {5,6} }
{ {7,6}, {3,4}, {5,3}, {2,3} }
{ {8,9}, {7,2}, {3,4}, {5,1} }

8 9
7 2
3 4
5 1
7 6
3 4
5 3
2 3
2 4
7 8
3 4
5 6
0th 2D Array
1st 2D Array
2nd 2D Array

A program to prints multi-dimension arrays

Relationship between array and pointer
 A consecutive series of variables that share one name which is int num [5];
 5 consecutive variables of integer type under the name of num
Which address does each element have?

Relationship between array and pointer
Int num [5];
&num[0] == 1000
&num[1] == 1004
&num[2] == 1008
&num[3] == 1012
&num[4] == 1016

Arithmetic of pointers
 “pointer +1” does not mean increasing pointer by 1
 “pointer + 1” is the address of the next element
 “pointer -1” is the address of the prior element
Relationship between array and pointer
Int num [5];
Num == &num[0] == 1000
&num[0] == 1000
&num[1] == 1004
&num[2] == 1008
&num[3] == 1012
&num[4] == 1016

Pointer arithmetic and element size
Adding an integer to a pointer

Pointer arithmetic and element size
Subtracting an integer to a pointer

Pointer arithmetic and element size
Subtracting pointer

Pointer operation
Pointer arithmetic and element size

Combining the * and ++ / -- operators
*++p = *(++p), *--p = *(--p)
- P increased or decreased then *p performed
*p++ = *(p++), *p-- = *(p--)
-p increased or decreased then *(p-1) or *(p+1) performed
(*p)++, (*p)—
-increased or decreased 1 of a variable pointing p

Combining the * and ++ operators

Combining the * and - - operators

Add input integer numbers Int num [ ] and int
*num are the same

Summary

Summary
 An array is a collection of similar elements
The 1st element in the array is numbered as 0, the last element is 1 less than the size of
the array. Example, name [20]. Which is the 1st element and last element?
Am array is also known as a subscripted variable.
Before using an array, its type and dimension must be declared. Example, int Marks
[30].
How big an array, its element are always stored in contiguous memory location, [ ]
 Pointer arithmetic can be added or subtracted
 Combining the * and - - operators in pointer