C#, check whether integer array has negative numbers in it

If you're open to using LINQ:

var containsNegatives = numArray.Any(n => n < 0);

Or, if you want to do it the "old fashioned" way...you just have to loop:

var containsNegatives = false;

foreach(var n in numArray)
{
    if(n < 0)
    {
        containsNegatives = true;
        break;
    }
}

And if you really want to get fancy, you could turn that into an Extension method:

public static class EnumerableExtensions
{
    public static bool ContainsNegatives(this IEnumerable<int> numbers)
    {
        foreach(n in numbers)
        {
            if(n < 0) return true;
        }

        return false;
    }
}

And call it from your code like:

var containsNegatives = numArray.ContainsNegatives();

var negativeExist = numArray.Any(a => a < 0);

You can use Array.Find(T) method to perform this task.

public static T Find<T>(
    T[] array,
    Predicate<T> match
)

For example,

using System;
using System.Drawing;

public class Example
{
    public static void Main()
    {
        // Create an array of five Point structures.
        Point[] points = { new Point(100, 200), 
            new Point(150, 250), new Point(250, 375), 
            new Point(275, 395), new Point(295, 450) };

        // To find the first Point structure for which X times Y 
        // is greater than 100000, pass the array and a delegate
        // that represents the ProductGT10 method to the static 
        // Find method of the Array class. 
        Point first = Array.Find(points, ProductGT10);

        // Note that you do not need to create the delegate 
        // explicitly, or to specify the type parameter of the 
        // generic method, because the C# compiler has enough
        // context to determine that information for you.

        // Display the first structure found.
        Console.WriteLine("Found: X = {0}, Y = {1}", first.X, first.Y);
    }

    // This method implements the test condition for the Find
    // method.
    private static bool ProductGT10(Point p)
    {
        if (p.X * p.Y > 100000)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

/* This code example produces the following output:

Found: X = 275, Y = 395
 */

Traditional:

foreach (int number in numArray) { if (number < 0) return true; }
return false;

With LINQ:

bool result = numArray.Any(x => x < 0);

A bit twidling version would be

public static bool AnyNegative(int[] arr){
  const long firstBit = 2147483648;
  var res = false;
  for (var i = 0; i < arr.Length && !res; i++) res = (arr[i] & firstBit) == firstBit;
  return res;
}

you can the call it like this>

int arr = {...}
  if(arr.AnyNegative()){
      //do stuf if there's any negative numbers
  }

of course this is just an obfuscated version of

public static bool AnyNegative(int[] arr){
            var res = false;
            for (var i = 0; i < arr.Length && !res; i++) res = arr[i] < 0;
            return res;
}