C# Program for Linear Search with Example and Explanation

A C# program for linear search uses a for loop to check each element in an array until it finds the target value, like for (int i = 0; i < arr.Length; i++) { if (arr[i] == target) return i; }.

Examples

Inputarray = {1, 2, 3, 4, 5}, target = 3

OutputElement found at index 2

Inputarray = {10, 20, 30, 40}, target = 25

OutputElement not found

Inputarray = {}, target = 1

OutputElement not found

How to Think About It

To do a linear search, start from the first item in the list and check if it matches the target. If it does, stop and return the position. If not, move to the next item and repeat until you find the target or reach the end.

Algorithm

1

Get the array and the target value.

2

Start from the first element in the array.

3

Compare the current element with the target.

4

If they match, return the current index.

5

If not, move to the next element.

6

If the end is reached without a match, return -1.

Code

csharp

using System;
class Program {
    static int LinearSearch(int[] arr, int target) {
        for (int i = 0; i < arr.Length; i++) {
            if (arr[i] == target) {
                return i;
            }
        }
        return -1;
    }
    static void Main() {
        int[] numbers = { 5, 3, 8, 4, 2 };
        int target = 4;
        int result = LinearSearch(numbers, target);
        if (result != -1) {
            Console.WriteLine("Element found at index " + result);
        } else {
            Console.WriteLine("Element not found");
        }
    }
}

Output

Element found at index 3

Dry Run

Let's trace searching for 4 in the array {5, 3, 8, 4, 2} through the code.

1

Start loop at index 0

Check if arr[0] (5) == 4? No, continue.

2

Check index 1

Check if arr[1] (3) == 4? No, continue.

3

Check index 2

Check if arr[2] (8) == 4? No, continue.

4

Check index 3

Check if arr[3] (4) == 4? Yes, return index 3.

Index	Value	Target	Match?
0	5	4	No
1	3	4	No
2	8	4	No
3	4	4	Yes

Why This Works

Step 1: Loop through array

The for loop goes through each element one by one to check for the target.

Step 2: Compare elements

Each element is compared with the target using == to find a match.

Step 3: Return index or -1

If a match is found, the index is returned; otherwise, -1 means not found.

Alternative Approaches

Using while loop

csharp

using System;
class Program {
    static int LinearSearch(int[] arr, int target) {
        int i = 0;
        while (i < arr.Length) {
            if (arr[i] == target) return i;
            i++;
        }
        return -1;
    }
    static void Main() {
        int[] numbers = { 1, 2, 3 };
        int target = 2;
        int result = LinearSearch(numbers, target);
        Console.WriteLine(result != -1 ? "Element found at index " + result : "Element not found");
    }
}

Uses a while loop instead of for; same logic but different loop style.

Using Array.IndexOf method

csharp

using System;
class Program {
    static void Main() {
        int[] numbers = { 7, 8, 9 };
        int target = 8;
        int index = Array.IndexOf(numbers, target);
        if (index != -1) Console.WriteLine("Element found at index " + index);
        else Console.WriteLine("Element not found");
    }
}

Uses built-in method for simplicity but less control over search process.

Complexity: O(n) time, O(1) space

Time Complexity

The search may check each element once, so time grows linearly with array size.

Space Complexity

No extra space is needed besides variables, so space is constant.

Which Approach is Fastest?

Using Array.IndexOf is fastest for simple searches, but manual loops give more control.

Approach	Time	Space	Best For
For loop linear search	O(n)	O(1)	Simple, clear control
While loop linear search	O(n)	O(1)	Alternative loop style
Array.IndexOf method	O(n)	O(1)	Quick built-in search