错误：操作员'！' 不能应用于'int'类型的操作数

Question

I am newbie to C sharp programming and was writing the program to determine whether a number is power of 2 or not. But getting error as Operator '!' cannot be applied to operand of type int. Thought the same program works well in C++. Here is the code:

    public static void Main(String[] args)
    {
        int x;

        Console.WriteLine("Enter the number: ");

        x = Convert.ToInt32(Console.ReadLine());


        if((x != 0) && (!(x & (x - 1))))

            Console.WriteLine("The given number "+x+" is a power of 2");
    }

Answer 1

In C#, the value 0 does not equal false , and different than 0 does not equal true , which is the case in C++.

For example, this expression is valid in C++ but not C# : while(1){} . You must use while(true) .

---

The operation x & (x - 1) gives an int (int bitwise AND int) so it's not converted to boolean by default.

To convert it to a bool , you may add the == or != operator to your expression.

So your program can be converted to this :

public static void Main(String[] args)
{
    int x;

    Console.WriteLine("Enter the number: ");
    x = Convert.ToInt32(Console.ReadLine());

    if((x != 0) && ((x & (x - 1)) == 0))
        Console.WriteLine("The given number "+x+" is a power of 2");
}

I used == 0 to remove the ! , but !((x & (x - 1)) != 0) would also be valid.

Answer 2

I got the answer by assigning boolean type to the expression and replace '!' with '-'

        public static void Main(String[] args)
        {
        int x;
        x = Convert.ToInt32(Console.ReadLine());
        bool y = ((x!=0) && -(x & (x-1))==0);
        if(y)
            Console.WriteLine("The given number is a power of 2");
        else
            Console.WriteLine("The given number is not a power of 2");
        Console.Read();