Searching Algorithm 1: Linear search or Sequential Search

In this chapter we shall learn about below topics:

Linear search is a search algorithm, that checks for the key in a set of values one by one till it reaches the end of all the elements.

For example:

Consider the array [14, 96, 27, 5, 48], and we need to search for the number 48. Below are the number of iterations necessary:

Consider the array given below and the key is 48.

[14, 96, 27, 5, 48]

if key == a[0]
else if key == a[1]
else if key == a[2]
else if key == a[3]
else if key == a[4]

If the key is found we shall display the index of the key, else we return key not found.

Input:

array
array_len
key

Algorithm:

linearSearch(arr, len, key)

	for i = 0 to n-1 
		if (arr[i] == key)
			return i
		end if
	end for

return -1; // key not found	 

#include<stdio.h>

void linearSearch(int *array, int len, int key)
{

	int i = 0;
	
//Iterate one by one to find the key
	for(i = 0; i< len ; i++ )
	{	
	//check one by one if the data at the index is same as key
		if(array[i] == key) 
		{
			printf("Key found at index = %d\n", i+1);
			return; //return statement is important. 
				//else it will continue to loop after the element is found
		}
	}
	printf("Not able to find key\n");

}

int main()
{
	int arr[5] = {10, 30, 48, 45, 78};

	int arrayLen = 5;

	int key = 45;

	int key_2 = 34;

//successful search
	linearSearch(arr,arrayLen, key);

//key not found case
	linearSearch(arr,arrayLen, key_2);

return 0;
}

Key found at index = 4
Not able to find key

Time complexity is O(n).