C# Program to Find Largest Number in Array

To find the largest number in an array in C#, use a loop to compare each element and keep track of the maximum value, like int max = arr[0]; foreach (int num in arr) { if (num > max) max = num; }.

Examples

Input[3, 5, 1, 9, 2]

Output9

Input[10, 10, 10]

Output10

Input[-5, -1, -10]

Output-1

How to Think About It

To find the largest number, start by assuming the first number is the largest. Then check each number one by one. If you find a number bigger than your current largest, update it. At the end, the largest number you have is the biggest in the array.

Algorithm

1

Start with the first element as the largest number.

2

Go through each number in the array.

3

If the current number is bigger than the largest, update the largest.

4

After checking all numbers, return the largest number.

Code

csharp

using System;
class Program {
    static void Main() {
        int[] arr = {3, 5, 1, 9, 2};
        int max = arr[0];
        foreach (int num in arr) {
            if (num > max) {
                max = num;
            }
        }
        Console.WriteLine(max);
    }
}

Output

9

Dry Run

Let's trace the array [3, 5, 1, 9, 2] through the code to find the largest number.

1

Initialize max

max = 3 (first element)

2

Compare with 5

5 > 3, so max = 5

3

Compare with 1

1 > 5? No, max stays 5

4

Compare with 9

9 > 5, so max = 9

5

Compare with 2

2 > 9? No, max stays 9

6

Result

Largest number is 9

Current Number	max Value
3	3
5	5
1	5
9	9
2	9

Why This Works

Step 1: Start with first element

We assume the first number is the largest to have a starting point for comparison.

Step 2: Compare each element

We check each number using if (num > max) to find if it is bigger than the current largest.

Step 3: Update largest value

When a bigger number is found, we update max to that number to keep track of the largest.

Step 4: Final largest number

After checking all numbers, max holds the largest number in the array.

Alternative Approaches

Using LINQ Max() method

csharp

using System;
using System.Linq;
class Program {
    static void Main() {
        int[] arr = {3, 5, 1, 9, 2};
        int max = arr.Max();
        Console.WriteLine(max);
    }
}

This is the shortest and most readable way but requires using LINQ and may be less clear for beginners.

Using for loop with index

csharp

using System;
class Program {
    static void Main() {
        int[] arr = {3, 5, 1, 9, 2};
        int max = arr[0];
        for (int i = 1; i < arr.Length; i++) {
            if (arr[i] > max) {
                max = arr[i];
            }
        }
        Console.WriteLine(max);
    }
}

This uses a classic for loop instead of foreach, useful if you need the index for other reasons.

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

Time Complexity

The program checks each element once, so the time grows linearly with the array size, making it O(n).

Space Complexity

Only a few variables are used regardless of input size, so space complexity is O(1).

Which Approach is Fastest?

Using a simple loop or LINQ's Max() both run in O(n) time, but LINQ is more concise while loops give more control.

Approach	Time	Space	Best For
Foreach loop	O(n)	O(1)	Clear logic and beginner-friendly
For loop with index	O(n)	O(1)	When index is needed for extra logic
LINQ Max()	O(n)	O(1)	Concise code and readability