C# Online Compiler | .NET Fiddle

using System;
					
public class Program
{
	public static void Main()
	{
		Console.WriteLine("Nhập x:");
		int x = int.Parse(Console.ReadLine());
		
		Console.WriteLine("Nhập số mũ n:");
		int n = int.Parse(Console.ReadLine());
		if(n>= 0)
			Console.WriteLine("Kết quả {0} mũ {1} là: {2}",x,n,power(x,n));
		else
			Console.WriteLine("Chương trình chỉ hỗ trợ tính số mũ dương");
	}
	static int power(int x, int n)
	{
		if (x==0)
		{
			return 0;
		}
		else if(n==0)
		{
			return 1;
		}
		else 
		{
			return x* power(x,n-1);//Gọi đệ quy
		}
	}
}

 
using System;
                    
public class Program
{
    public static void Main()
    {
        Console.WriteLine("Nhập x:");
        int x = int.Parse(Console.ReadLine());
        
        Console.WriteLine("Nhập số mũ n:");
        int n = int.Parse(Console.ReadLine());
        if(n>= 0)
            Console.WriteLine("Kết quả {0} mũ {1} là: {2}",x,n,power(x,n));
        else
            Console.WriteLine("Chương trình chỉ hỗ trợ tính số mũ dương");
    }
    static int power(int x, int n)
    {
        if (x==0)
        {
            return 0;
        }
        else if(n==0)
        {
            return 1;
        }
        else 
        {
            return x* power(x,n-1);//Gọi đệ quy
        }
    }
}

Compilation error (line 6, col 38): Newline in constant
Compilation error (line 6, col 38): Too many characters in character literal
Compilation error (line 10, col 54): Newline in constant
Compilation error (line 12, col 54): Newline in constant
Compilation error (line 13, col 54): Newline in constant
Compilation error (line 14, col 52): Newline in constant
Compilation error (line 82, col 17): Too many characters in character literal
Compilation error (line 105, col 17): Too many characters in character literal
Compilation error (line 123, col 29): Newline in constant
Compilation error (line 141, col 21): Too many characters in character literal
Compilation error (line 157, col 17): Too many characters in character literal
Compilation error (line 169, col 25): Too many characters in character literal
Compilation error (line 190, col 13): Too many characters in character literal
Compilation error (line 193, col 29): Newline in constant
Compilation error (line 204, col 17): Too many characters in character literal
Compilation error (line 223, col 29): Newline in constant
Compilation error (line 1, col 1): A namespace cannot directly contain members such as fields or methods