C#: Find the missing number in a given array of numbers between 10 and 20

Last update on August 22 2025 12:42:32 (UTC/GMT +8 hours)

Write a C# Sharp program to find the missing number in a given array of numbers between 10 and 20.

Sample Solution:-

C# Sharp Code:

using System;
using System.Linq;

namespace exercises
{
    class Program
    {
        static void Main(string[] args)
        {
            // Initializing an array of integers
            int[] nums = { 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 };

            // Displaying original array elements
            Console.WriteLine("Original array elements:");
            Array.ForEach(nums, Console.WriteLine);

            // Finding the missing number in the array (10-20) using the test method
            Console.WriteLine("Missing number in the said array (10-20): " + test(nums));

            // Creating additional arrays with missing elements and testing the 'test' method
            int[] nums1 = { 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 };
            Console.WriteLine("\nOriginal array elements:");
            Array.ForEach(nums1, Console.WriteLine);
            Console.WriteLine("Missing number in the said array (10-20): " + test(nums1));

            int[] nums2 = { 10, 11, 12, 13, 14, 16, 17, 18, 19, 20 };
            Console.WriteLine("\nOriginal array elements:");
            Array.ForEach(nums2, Console.WriteLine);
            Console.WriteLine("Missing number in the said array (10-20): " + test(nums2));

            int[] nums3 = { 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 };
            Console.WriteLine("\nOriginal array elements:");
            Array.ForEach(nums3, Console.WriteLine);
            Console.WriteLine("Missing number in the said array (10-20): " + test(nums3));
        }

        // Method to find the missing number in the array (10-20)
        public static int test(int[] arr)
        {
            // Returning the missing number by subtracting the sum of array elements from the expected sum
            return 165 - arr.Sum();
        }
    }
}

Sample Output:

Original array elements:
10
11
12
13
14
15
16
17
18
19
20
Missing number in the said array (10-20): 0

Original array elements:
11
12
13
14
15
16
17
18
19
20
Missing number in the said array (10-20): 10

Original array elements:
10
11
12
13
14
16
17
18
19
20
Missing number in the said array (10-20): 15

Original array elements:
10
11
12
13
14
15
16
17
18
19
Missing number in the said array (10-20): 20

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