Language: C++

// Elementary data structures - Stack
// hhttp://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_3_A
using System;
using System.Linq;
 
namespace ALDS1_3_A {
    class Program {
        public Program() {}
         
        public static void Main() {
            new Program().Calc();
        }
         
        void Calc() {
            var input = Input.Split(' ');
            var stack = new Stack<int>();
            int a, b;
            foreach (var str in input) {
                switch (str) {
                    case "+":
                        a = stack.pop();
                        b = stack.pop();
                        stack.Push(a + b);
                        break;
                    case "-":
                        a = stack.pop();
                        b = stack.pop();
                        stack.Push(b - a);
                        break;
                    case "*":
                        a = stack.pop();
                        b = stack.pop();
                        stack.Push(a * b);
                        break;
                    case "/":
                        a = stack.pop();
                        b = stack.pop();
                        stack.Push(b / a);
                        break;
                    default:
                        stack.Push(int.Parse(itstrem));
                        break;
                }
            }
            Output(stk.Pop());
        }
         
        String Input {
            get {
                return Console.ReadLine();
            }
        }
         
        void Output(String str) {
            Console.WriteLine(str);
        }
    }
}

Compiler output:
a.cc:3:7: error: expected nested-name-specifier before 'System'
    3 | using System;
      |       ^~~~~~
a.cc:4:7: error: expected nested-name-specifier before 'System'
    4 | using System.Linq;
      |       ^~~~~~
a.cc:8:15: error: expected ':' before 'Program'
    8 |         public Program() {}
      |               ^~~~~~~~
      |               :
a.cc:10:15: error: expected ':' before 'static'
   10 |         public static void Main() {
      |               ^~~~~~~
      |               :
a.cc:48:9: error: 'String' does not name a type
   48 |         String Input {
      |         ^~~~~~
a.cc:54:21: error: 'String' has not been declared
   54 |         void Output(String str) {
      |                     ^~~~~~
a.cc:57:6: error: expected ';' after class definition
   57 |     }
      |      ^
      |      ;
a.cc: In static member function 'static void ALDS1_3_A::Program::Main()':
a.cc:11:26: error: expected ';' before '.' token
   11 |             new Program().Calc();
      |                          ^
a.cc: In member function 'void ALDS1_3_A::Program::Calc()':
a.cc:15:13: error: 'var' was not declared in this scope
   15 |             var input = Input.Split(' ');
      |             ^~~
a.cc:16:17: error: expected ';' before 'stack'
   16 |             var stack = new Stack<int>();
      |                 ^~~~~
a.cc:18:26: error: expected ')' before 'str'
   18 |             foreach (var str in input) {
      |                          ^~~
a.cc:18:21: note: to match this '('
   18 |             foreach (var str in input) {
      |                     ^
a.cc:18:13: error: 'foreach' was not declared in this scope
   18 |             foreach (var str in input) {
      |             ^~~~~~~
a.cc:45:20: error: 'stk' was not declared in this scope; did you mean 'std'?
   45 |             Output(stk.Pop());
      |                    ^~~
      |                    std
a.cc: In member function 'void ALDS1_3_A::Program::Output(int)':
a.cc:55:13: error: 'Console' was not declared in this scope
   55 |             Console.WriteLine(str);
      |             ^~~~~~~