Linear Search Algorithm Explained: Definition and Implementation

Linear search is a sequential searching algorithm where we start from one end and check every element of the list until the desired element is found. It is the simplest searching algorithm.

Algorithm

Linear Search ( Array A, Value x)

Step 1: Set i to 1
Step 2: if i > n then go to step 7
Step 3: if A[i] = x then go to step 6
Step 4: Set i to i + 1
Step 5: Go to Step 2
Step 6: Print Element x Found at index i and go to step 8
Step 7: Print element not found
Step 8: Exit

Pseudocode

 
procedure linear_search (list, value)

   for each item in the list
      if match item == value
         return the item's location
      end if
   end for

end procedure

Linear search in C programming: The following code implements linear search (Searching algorithm) which is used to find whether a given number is present in an array and if it is present then at what location it occurs. It is also known as sequential search. It is straightforward and works as follows: We keep on comparing each element with the element to search until it is found or the list ends. Linear search in C language for multiple occurrences and using function.

Linear search C program

 
#include <stdio.h>
 
int main()
{
  int array[100], search, c, n;
 
  printf("Enter the number of elements in array\n");
  scanf("%d", &n);
 
  printf("Enter %d integer(s)\n", n);
 
  for (c = 0; c < n; c++)
    scanf("%d", &array[c]);
 
  printf("Enter a number to search\n");
  scanf("%d", &search);
 
  for (c = 0; c < n; c++)
  {
    if (array[c] == search)    /* If required element is found */
    {
      printf("%d is present at location %d.\n", search, c+1);
      break;
    }
  }
  if (c == n)
    printf("%d isn't present in the array.\n", search);
 
  return 0;
}

 

Output:

Enter the number of elements in array
10
Enter 10 integer(s)
9
6
8
6
2
2
7
8
66
23
Enter a number to search
23
23 is present at location 10.
Press any key to continue . . .
 

Linear search for multiple occurrences

In the code below we will print all the locations at which required element is found and also the number of times it occur in the list.

 
 #include <stdio.h>
 
int main()
{
   int array[100], search, c, n, count = 0;
 
   printf("Enter the number of elements in array\n");
   scanf("%d", &n);
 
   printf("Enter %d numbers\n", n);
 
   for (c = 0; c < n; c++)
      scanf("%d", &array[c]);
 
   printf("Enter the number to search\n");
   scanf("%d", &search);
 
   for (c = 0; c < n; c++) {
      if (array[c] == search) {
         printf("%d is present at location %d.\n", search, c+1);
         count++;
      }
   }
   if (count == 0)
      printf("%d isn't present in the array.\n", search);
   else
      printf("%d is present %d times in the array.\n", search, count);
 
   return 0;
}

 

Output

 Enter the number of elements in array
10
Enter 10 numbers
9
8
7
6
5
3
3
2
1
3
Enter the number to search
3
3 is present at location 6.
3 is present at location 7.
3 is present at location 10.
3 is present 3 times in the array.
Press any key to continue . . .
 

C program for linear search using function

   
 #include <stdio.h>
 
long linear_search(long [], long, long);
 
int main()
{
   long array[100], search, c, n, position;
 
   printf("Input number of elements in array\n");
   scanf("%ld", &n);
 
   printf("Input %d numbers\n", n);
 
   for (c = 0; c < n; c++)
      scanf("%ld", &array[c]);
 
   printf("Input number to search\n");
   scanf("%ld", &search);
 
   position = linear_search(array, n, search);
 
   if (position == -1)
      printf("%d isn't present in the array.\n", search);
   else
      printf("%d is present at location %d.\n", search, position+1);
 
   return 0;
} 
 
long linear_search(long a[], long n, long find) {
   long c;
 
   for (c = 0 ;c < n ; c++ ) {
      if (a[c] == find)
         return c;
   }
 
   return -1;
}

 

Output:

 Input number of elements in array
10
Input 10 numbers
9
8
7
6
5
3
2
1
10
2
Input number to search
3
3 is present at location 6.
Press any key to continue . . .
 

Linear search function using pointers

 
long linear_search(long *pointer, long n, long find)
{
   long c;
 
   for (c = 0; c < n; c++) {
      if (*(pointer+c) == find)
         return c;
   }
 
   return -1;
}
 

The time required to search an element using linear search algorithm depends on the size of the list. In the best case it is present at beginning of the list and in the worst case element is present at the end. The time complexity of linear search is O(n).