Arrays

Arrays in C
 OUTLINE

♦ Review of Arrays in C
♦ Declaration and Initialization of Arrays
♦ Sorting: Bubble Sort
♦ Searching: Linear and Binary Search

Arrays
 Arrays are defined to be a sequence/set of data
elements of the same type. Having an array, each
array element can be accessed by its position in the
sequence of the array.
♦ Decleration of the Arrays: Any array declaration
contains: the array name, the element type and the
array size.
 Examples:
 int a[20], b[3],c[7];
 float f[5], c[2];
 char m[4], n[20];

Arrays
 Initialisation of an array is the process of
assigning initial values. Typically declaration
and initialisation are combined.
 Examples:
 int a[4]={1,3,5,2};
 float, b[3]={2.0, 5.5, 3.14};
 char name[4]= {‘E’,’m’,’r’,’e’};
 int c[10]={0};

Example
 Write a program to calculate and print the average of the following array
of integers.
 ( 4, 3, 7, -1, 7, 2, 0, 4, 2, 13)
 #include<stdio.h>
 #define size 10
 int main()
 {
 int x[10]={4,3,7,-1,7,2,0,4,2,13}, i, sum=0;
 float av;
 for(i=0,i<=size-1;i++)
 sum = sum + x[i];
 av = (float)sum/size;
 printf(“The average of the numbers=%.2fn”, av);
 return 0;
 }

Sorting
 Sorting an array is the ordering the array elements
in ascending (increasing -from min to max) or
descending (decreasing – from max to min) order.
 Example:
 {2 1 5 3 2} →{1, 2, 2, 3, 5} ascending order
 {2 1 5 3 2} →{5, 3, 2, 2, 1} descending order

Bubble Sort
 Smaller values in the list gradually “bubble”
their way upward to the top of the array.
 The technique makes several passes through
the array. On each pass successive pairs of
elements are compared. If the pair is in
increasing order (or equal) the pair is
unchanged. If a pair is in descending order,
their values are swapped in the array:

Bubble Sort
Pass = 1 Pass = 2 Pass = 3 Pass=4

21532 12325 12235 12235

12532 12325 12235 12235

12532 12325 12235 12235

12352 12235 12235 12235

12325 12235 12235 12235
Underlined pairs show the comparisons. For each pass there are size-1
comparisons.
Total number of comparisons= (size-1)2

Bubble Sort C Code
 /* This program sorts the array elements in the ascending order*/
 #include <stdio.h>
 #define SIZE 5
 void BubbleSort(int [ ]);
 int main()
 {
 int a[SIZE]= {2,1,5,3,2};
 int i;
 printf(“The elements of the array before sortingn”);
 for (i=0; i<= SIZE-1; i++)
 printf(“%4d”, a[i]);
 BubbleSort(a);
 printf(“nnThe elements of the array after sortingn”);
 for (i=0; i<= SIZE-1; i++)
 printf(“%4d”, a[i]);
 return 0;
 }

void BubbleSort(int A[ ])
 void BubbleSort(int A[ ])
 {
 int i, pass, hold;
 for (pass=1; pass<= SIZE-1; pass++){
 for (i=0; i<= SIZE-2; i++) {
 if(A[i] >A[i+1]){
 hold =A[i];

 A[i]=A[i+1];

 A[i+1]=hold;

 }

 }
 }
 }

Example
 Write a program to determine the median of
the array given below:
(9, 4, 5, 1, 7, 78, 22, 15, 96, 45)
 Note that the median of an array is the middle
element of a sorted array.

Example
/* This program determines the median of an array*/
#include <stdio.h>
#define SIZE 10
void BubbleSort(int []);
int main()
{
int a[SIZE]= {9, 4, 5, 1, 7, 78, 22, 15, 96, 45}, median;
int i;
printf(“The elements of the input array isn”);
for (i=0; i<= SIZE-1; i++)
printf(“%4d”, a[i]);
BoubleSort(a);
printf(“The elements of the sorted array isn”);
for (i=0; i<= SIZE-1; i++)
printf(“%4d”, a[i]);
median = a[SIZE/2];
printf(“The median of the array is=%d”, median);
return 0;
}

Example
void BubbleSort(int A[ ])
{
int i, pass, hold;
for (pass=1; pass<= SIZE-1; pass++){
for (i=0; i<= SIZE-2; i++) {
if(A[i] >A[i+1]){
hold =A[i];
A[i]=A[i+1];
A[i+1]=hold;
}
}
}
}

Searching
 The process of finding a particular element of an
array is called searching. There two popularsearching
techniques:
 Linear search and binary search.
 The linear search compares each array element with
the search key.
 If the search key is a member of the array, typically
the location of the search key is reported to indicate
the presence of the search key in the array.
Otherwise, a sentinel value is reported to indicate the
presence of the search key in the array.

Linear Search
 Each member of the array is visited until the
search key is found.
 Example:
 Write a program to search for the search key
entered by the user in the following array:
(9, 4, 5, 1, 7, 78, 22, 15, 96, 45)
 You can use the linear search in this
example.

Linear Search
 /* This program is an example of the Linear Search*/
 #include <stdio.h>
 #define SIZE 10
 int LinearSearch(int [], int);
 int main()
 {
 int a[SIZE]= {9, 4, 5, 1, 7, 78, 22, 15, 96, 45}, key, pos;
 printf(“Enter the Search Keyn”);
 scanf(“%d”,&key);
 pos = LinearSearch(a, key);
 if(pos == -1)
 printf(“The search key is not in the arrayn”);
 else
 printf(“The search key %d is at location %dn”, key, pos);
 return 0;
 }

int LinearSearch (int b[ ], int skey)
int LinearSearch (int b[ ], int skey)
{
int i;
for (i=0; i<= SIZE-1; i++)
if(b[i] == skey)
return i;
return -1;
}

Binary Search
 Given a sorted array Binary Search
algorithm can be used to perform fast
searching of a search key on the sorted array.
 The following program uses pointer notation
to implement the binary search algorithm for
the search key entered by the user in the
following array:
(3, 5, 9, 11, 15, 17, 22, 25, 37, 68)

Binary Search
#include <stdio.h>
#define SIZE 10
int BinarySearch(int [ ], int);
int main()
{
int a[SIZE]= {3, 5, 9, 11, 15, 17, 22, 25, 37, 68}, key, pos;
printf(“Enter the Search Keyn”);
scanf(“%d”,&key);
pos = BinarySearch(a, key);
if(pos == -1)
printf(“The search key is not in the arrayn”);
else
printf(“The search key %d is at location %dn”, key, pos);
return 0;
}

int BinarySearch (int A[], int skey)
int BinarySearch (int A[], int skey)
{
int low=0,high=SIZE-1,middle;
while(low <= high){
middle= (low+high)/2;
if(skey == A[middle])
return middle;
else if(skey <A[middle])
high = middle-1;
else
low = middle+1;
}
return -1;
}

Computational Complexity
 The Computational Complexity of the Binary
Search algorithm is measured by the maximum
(worst case) number of Comparisons it performs for
searching operations.
 The searched array is divided by 2 for each
comparison/iteration.
 Therefore, the maximum number of comparisons is
measured by:
 log2(n) where n is the size of the array
 Example:
 If a given sorted array 1024 elements, then the
maximum number of comparisons required is:
 log2(1024) = 10 (only 10 comparisons is enough)

Computational Complexity
 Note that the Computational Complexity of the
Linear Search is the maximum number of
comparisons you need to search the array. As you
are visiting all the array elements in the worst case,
then, the number of comparisons required is:
n (n is the size of the array)
 Example:
 If a given an array of 1024 elements, then the
maximum number of comparisons required is:
n = 1024 (As many as 1024 comparisons may be
required)

Arrays

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Arrays