Binary search in C: solved exercise on sorted arrays

Binary search in C: solved exercise

If you searched for binary search in C solved exercise, this page includes a clean iterative implementation and complexity notes.

Problem statement

Given a sorted array, return the target index or -1 if missing.

C solution

#include <stdio.h>

int binary_search(int a[], int n, int target) {
    int l = 0, r = n - 1;

    while (l <= r) {
        int m = l + (r - l) / 2;

        if (a[m] == target) return m;
        if (a[m] < target) l = m + 1;
        else r = m - 1;
    }

    return -1;
}

int main(void) {
    int a[] = {2, 5, 9, 12, 18, 25};
    int idx = binary_search(a, 6, 12);

    printf("Index: %d\n", idx);
    return 0;
}

Expected output

Index: 3

Complexity

• Time: O(log n)
• Space: O(1)

Common mistakes

• Running it on unsorted arrays.
• Wrong midpoint calculation.
• Incorrect range updates (l, r).

Practical use

Binary search appears in ordered catalogs, index systems, and high-performance query paths.

Recommended next exercise

• Merge sort in C: solved exercise with divide and conquer
• Bubble sort in C: solved exercise step by step
• Queue in C: solved exercise with circular array
• All C exercises

Guided practice and full book

If you want a complete path with progressive difficulty:

• Programming in C in 100 Solved Exercises
• View on Amazon (included in Kindle Unlimited)

FAQ

Is this exercise useful for C exams and technical interviews?

Yes. It targets patterns that commonly appear in practice assignments, technical interviews, and C programming exams.

Where can I keep practicing with more solved C exercises?

In Programming in C in 100 Solved Exercises and C Exercises. Kindle Unlimited: View on Amazon.

How should I practice this exercise type to improve faster?

Start with small inputs, run edge cases (empty, one item, max capacity), then rewrite the solution from scratch without copying.