Searching Algorithms in C

In the previous lesson, you learned how to arrange data using sorting algorithms.

Once data is organized, the next important task is to find a specific value from the data.

This process is called Searching.

What Is Searching?

Searching means checking whether a particular element exists in a data set.

Examples:

• Finding a roll number in a list
• Searching a contact in a phone
• Checking a value in an array

Types of Searching Algorithms

• Linear Search
• Binary Search

We will understand both clearly using C programs.

Linear Search

Linear search checks each element one by one.

It works on both sorted and unsorted data.

#include <stdio.h>

int main() {
    int a[5] = {10, 25, 30, 45, 50};
    int key = 30;
    int i, found = 0;

    for (i = 0; i < 5; i++) {
        if (a[i] == key) {
            found = 1;
            break;
        }
    }

    if (found)
        printf("Element found at position %d", i + 1);
    else
        printf("Element not found");

    return 0;
}

Linear search is simple but slow for large data.

Binary Search

Binary search works only on sorted data.

It repeatedly divides the search range into half.

#include <stdio.h>

int main() {
    int a[5] = {10, 20, 30, 40, 50};
    int key = 40;
    int low = 0, high = 4, mid;
    int found = 0;

    while (low <= high) {
        mid = (low + high) / 2;

        if (a[mid] == key) {
            found = 1;
            break;
        }
        else if (key < a[mid])
            high = mid - 1;
        else
            low = mid + 1;
    }

    if (found)
        printf("Element found at position %d", mid + 1);
    else
        printf("Element not found");

    return 0;
}

Linear vs Binary Search

• Linear search is simple but slow
• Binary search is fast but needs sorted data

Real-World Example

Searching a name in:

• Unsorted list → Linear Search
• Dictionary → Binary Search

Mini Practice

• Take 10 numbers from user
• Search a number using linear search
• Then sort the array and apply binary search

Quick Quiz

Q1. What is searching?

Finding a specific element in data

Q2. Which search works on unsorted data?

Linear Search

Q3. Binary search requires what?

Sorted data

Q4. Binary search divides data into?

Two halves

Q5. Which search is faster for large data?

Binary Search