Searching Algorithms in C (Complete Guide with Examples)

This tutorial explains searching algorithms in C, which are used to find an element in a data structure. It covers Linear Search and Binary Search with practical examples, helping improve problem-solving and algorithmic skills.

1. What is Searching

  1. Searching is the process of finding the position of an element in a data structure
  2. Common types of searching:
  3. Linear Search – Sequentially check each element
  4. Binary Search – Efficient search in sorted data using divide and conquer

2. Linear Search

  1. Traverse the array one by one until the element is found
  2. Works on both sorted and unsorted arrays

Example: Linear Search


#include <stdio.h>

int linearSearch(int arr[], int n, int key) {
for(int i = 0; i < n; i++) {
if(arr[i] == key)
return i; // element found at index i
}
return -1; // element not found
}

int main() {
int arr[] = {5, 2, 9, 1, 5};
int n = sizeof(arr)/sizeof(arr[0]);
int key = 9;

int result = linearSearch(arr, n, key);
if(result != -1)
printf("Element %d found at index %d\n", key, result);
else
printf("Element not found\n");

return 0;
}

Output:


Element 9 found at index 2

3. Binary Search

  1. Works on sorted arrays only
  2. Repeatedly divides the array into two halves and compares with mid element

Example: Binary Search


#include <stdio.h>

int binarySearch(int arr[], int n, int key) {
int low = 0, high = n - 1;

while(low <= high) {
int mid = low + (high - low)/2;
if(arr[mid] == key)
return mid;
else if(arr[mid] < key)
low = mid + 1;
else
high = mid - 1;
}
return -1; // element not found
}

int main() {
int arr[] = {1, 2, 5, 5, 9};
int n = sizeof(arr)/sizeof(arr[0]);
int key = 5;

int result = binarySearch(arr, n, key);
if(result != -1)
printf("Element %d found at index %d\n", key, result);
else
printf("Element not found\n");

return 0;
}

Output:


Element 5 found at index 2

4. Key Points to Remember

  1. Linear Search: O(n), works on unsorted arrays, simple to implement
  2. Binary Search: O(log n), requires sorted array, very efficient for large datasets
  3. Always ensure array is sorted before using Binary Search
  4. Searching is the foundation for advanced algorithms and data structures