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C Program To Implement Linear Search.

The following code implements linear search (Searching algorithm) which is used to find whether a given number is present in an array or not and if it is present then at what location it occurs. It is also known as sequential search. It is very simple and works as follows: we keep on comparing each element with the element to search until the desired element is found. Time required to search an element using linear search algorithm depends on the size of list. In the best case, element is present at the beginning of list and in the worst case, element is present at the end. Time complexity of linear search is O(n). 

#include <stdio.h>

int main() {
int array[100], search, c, n;

printf("\nEnter the number of elements in array: ");
scanf("%d",&n);

printf("\n\nEnter %d integer(s): \n", n);
for (c = 0; c < n; c++)
scanf("%d", &array[c]);

printf("\n\nEnter the number to search: ");
scanf("%d", &search);

for (c = 0; c < n; c++) {
if (array[c] == search) {
printf("\n%d is present at location %d.\n\n", search, c+1);
break;
}}

if (c == n)
printf("\n%d is not present in array.\n\n", search);
return 0;
}

Linear search for multiple occurrences: n 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("\nEnter the number of elements in array: ");
scanf("%d", &n);

printf("\n\nEnter %d numbers: \n", n);
for ( c = 0 ; c < n ; c++ )
scanf("%d", &array[c]);

printf("\n\nEnter the number to search: ");
scanf("%d", &search);

for (c = 0; c < n; c++) {
if (array[c] == search) {
printf("\n%d is present at location %d.\n\n", search, c+1);
count++;
}}
if (count == 0)
printf("\n%d is not present in array.\n\n", search);
else
printf("\n%d is present %d times in array.\n\n", search, count);
return 0;
}

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: ");
scanf("%ld", &n);

printf("\n\nInput %d numbers: ", n);
for (c = 0; c < n; c++)
scanf("%ld", &array[c]);

printf("\n\nInput number to search: ");
scanf("%ld",&search);

position = linear_search(array, n, search);

if (position == -1)
printf("\n%d is not present in array.\n\n", search);
else
printf("\n%d is present at location %d.\n\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;
}

Linear search using pointer: copy the first part (L.S. with function)
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;
}
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