Binary Search in C and C++ – Run Online

What is Binary Search?

Binary search discards half of the remaining range after each comparison.

Search sorted data in logarithmic time.

Important points

Test empty, single-element, duplicate, and already sorted inputs.
Separate correctness from optimization.
Use the standard library in production unless a custom implementation is justified.

Binary Search visualizer

O(log n)

Use Play or Step to follow each comparison and data movement.

C and C++ code examples

C

Run code →

main.c

#include <stdio.h>

int search(const int *values, int size, int target) {
    int low = 0;
    int high = size - 1;
    while (low <= high) {
        int middle = low + (high - low) / 2;
        if (values[middle] == target) return middle;
        if (values[middle] < target) low = middle + 1;
        else high = middle - 1;
    }
    return -1;
}

int main(void) {
    int values[] = {3, 7, 11, 16, 23, 28};
    printf("index=%d\n", search(values, 6, 23));
}

Expected output

index=4

C++

Run code →

main.cpp

#include <algorithm>
#include <iostream>
#include <vector>

int main() {
    std::vector values{3, 7, 11, 16, 23, 28};
    auto match = std::lower_bound(values.begin(), values.end(), 23);
    std::cout << "index="
              << std::distance(values.begin(), match) << '\n';
}

Expected output

index=4

C and C++ comparison

The input must be sorted. The manual C loop and std::lower_bound both run in O(log n) on random-access ranges.

C

Loops, pointers, lengths, and temporary buffers are written explicitly.

C++

Iterators and standard algorithms separate operations from container representation.

Practice exercises

Run both versions, then modify them to observe the different language guarantees.

Trace each comparison on paper.
Test duplicates and extreme values.
Benchmark the custom implementation against the standard library.