Linear Search

Walk an array once looking for a target value. Return the index of the first match, or -1 if none. The simplest possible search loop.

Algorithm

Canonical input arr = [4, 7, 1, 9, 3, 8] with target = 9 finishes after four compares; the matching index is 3.

Basic Implementation

basic.c

#include <stdio.h>

int linearSearch(const int *arr, size_t n, int target) {
    for (size_t i = 0; i < n; ++i) {
        if (arr[i] == target) {
            return (int)i;
        }
    }
    return -1;
}

int main(void) {
    int arr[] = {4, 7, 1, 9, 3, 8};
    size_t n = sizeof(arr) / sizeof(arr[0]);
    int target = 9;
    int result = linearSearch(arr, n, target);
    printf("%d\n", result);
    return 0;
}

Complexity

Time: O(n)
Space: O(1)

Implementation notes

C: explicit for (size_t i = 0; i < n; ++i). C has no find helper — the lesson is teaching the walk directly.
Function signature int linearSearch(const int *arr, size_t n, int target) documents the integer-array contract; the (int)i cast makes the size/index sign discipline explicit.
The replay shows the running index, the element being checked, and a match indicator on each frame.

early exit Return the index the moment `arr[i]` equals the target. Walking past it would defeat the point.

sentinel return A no-match walk falls off the loop and returns `-1`.