The Binary Search Algorithm

This lesson covers implementing the binary search algorithm in C, so you understand how to search efficiently. It's for anyone searching "C binary search implementation."

Binary search is an algorithm for efficiently finding a target value in already-sorted data. It's like opening a dictionary somewhere near the middle and narrowing your search range in half from there.

The example computes the midpoint mid from two positions, low and high, comparing it against the target value and updating low or high to narrow the range. Compared to checking one element at a time from the start, this finds the target value dramatically faster the larger the dataset is.

A common early mistake is not realizing binary search requires the array to already be sorted beforehand. It's a precondition that the data you're searching is already sorted, so don't forget to sort it first.

In real projects, this idea is applied widely wherever you need to quickly find a specific value among a large amount of data.

📖 Reference code

#include <stdio.h>

int binarySearch(int arr[], int n, int target) {
    int low = 0, high = n - 1;
    while (low <= high) {
        int mid = (low + high) / 2;
        if (arr[mid] == target) return mid;
        if (arr[mid] < target) low = mid + 1;
        else high = mid - 1;
    }
    return -1;
}

int main(void) {
    int nums[] = {1, 3, 5, 7, 9, 11};
    printf("%d\n", binarySearch(nums, 6, 7));
    printf("%d\n", binarySearch(nums, 6, 4));
    return 0;
}

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run C directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).