Language: C++

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace __C__ProgramingContest
{
    class Program
    {
        static void Main(string[] args)
        {
            int num5 = 5;
            int num9 = 9;

            ////論理積
            //int numCalc = num5 & num9;

            //Console.Write(Convert.ToString(num5, 2).PadLeft(8, '0'));
            //Console.WriteLine("({0})", num5);

            //Console.Write(Convert.ToString(num9, 2).PadLeft(8, '0'));
            //Console.WriteLine("({0})", num9);

            //Console.WriteLine("{0} & {1} =", num5, num9);

            //Console.Write(Convert.ToString(numCalc, 2).PadLeft(8, '0'));
            //Console.WriteLine("({0})", numCalc);
            // 整数の入力
            int a = int.Parse(Console.ReadLine());
            int ans = 0;
            //int a = int.Parse(Console.ReadLine());
            // スペース区切りの整数の入力
            // 100個の要素を0で初期化（intをnewした場合はゼロクリアされる）
            int[] x = new int[100005];
            int[] y = new int[100005];
            int[] z = new int[100005];
            //int[,] count = new int[1003,1003];

            string[] input = Console.ReadLine().Split(' ');
            for (int i = 0; i < a; i++)
            {
                x[i] = int.Parse(input[i]);
            }
            for (int i = 0; i < a - 2; i++)
            {
                if ((x[i] < x[i + 1] && x[i + 1] < x[i + 2])
                    ||(x[i] > x[i + 1] && x[i + 1] > x[i + 2]))
                {
                    ans++;
                }
            }
            // 文字列の入力
            //string s = Console.ReadLine();
            //出力
            //Console.WriteLine((a + b) + " " + s);
            Console.WriteLine(ans);

        }
    }
}

Compiler output:
a.cc:1:7: error: expected nested-name-specifier before 'System'
    1 | using System;
      |       ^~~~~~
a.cc:2:7: error: expected nested-name-specifier before 'System'
    2 | using System.Collections.Generic;
      |       ^~~~~~
a.cc:3:7: error: expected nested-name-specifier before 'System'
    3 | using System.Linq;
      |       ^~~~~~
a.cc:4:7: error: expected nested-name-specifier before 'System'
    4 | using System.Text;
      |       ^~~~~~
a.cc:5:7: error: expected nested-name-specifier before 'System'
    5 | using System.Threading.Tasks;
      |       ^~~~~~
a.cc:11:26: error: 'string' has not been declared
   11 |         static void Main(string[] args)
      |                          ^~~~~~
a.cc:11:35: error: expected ',' or '...' before 'args'
   11 |         static void Main(string[] args)
      |                                   ^~~~
a.cc:60:6: error: expected ';' after class definition
   60 |     }
      |      ^
      |      ;
a.cc: In static member function 'static void __C__ProgramingContest::Program::Main(int*)':
a.cc:30:21: error: expected primary-expression before 'int'
   30 |             int a = int.Parse(Console.ReadLine());
      |                     ^~~
a.cc:35:16: error: structured binding declaration cannot have type 'int'
   35 |             int[] x = new int[100005];
      |                ^~
a.cc:35:16: note: type must be cv-qualified 'auto' or reference to cv-qualified 'auto'
a.cc:35:16: error: empty structured binding declaration
a.cc:35:19: error: expected initializer before 'x'
   35 |             int[] x = new int[100005];
      |                   ^
a.cc:36:16: error: structured binding declaration cannot have type 'int'
   36 |             int[] y = new int[100005];
      |                ^~
a.cc:36:16: note: type must be cv-qualified 'auto' or reference to cv-qualified 'auto'
a.cc:36:16: error: empty structured binding declaration
a.cc:36:19: error: expected initializer before 'y'
   36 |             int[] y = new int[100005];
      |                   ^
a.cc:37:16: error: structured binding declaration cannot have type 'int'
   37 |             int[] z = new int[100005];
      |                ^~
a.cc:37:16: note: type must be cv-qualified 'auto' or reference to cv-qualified 'auto'
a.cc:37:16: error: empty structured binding declaration
a.cc:37:19: error: expected initializer before 'z'
   37 |             int[] z = new int[100005];
      |                   ^
a.cc:40:13: error: 'string' was not declared in this scope
   40 |             string[] input = Console.ReadLine().Split(' ');
      |             ^~~~~~
a.cc:40:20: error: expected primary-expression before ']' token
   40 |             string[] input = Console.ReadLine().Split(' ');
      |                    ^
a.cc:43:17: error: 'x' was not declared in this scope
   43 |                 x[i] = int.Parse(input[i]);
      |                 ^
a.cc:43:24: error: expected primary-expression before 'int'
   43 |                 x[i] = int.Parse(input[i]);
      |                        ^~~
a.cc:47:22: error: 'x' was not declared in this scope
   47 |                 if ((x[i] < x[i + 1] && x[i + 1] < x[i + 2])
      |                      ^
a.cc:57:13: error: 'Console' was not declared in this scope
   57 |             Console.WriteLine(ans);
      |             ^~~~~~~