C＃变量已使用但从未分配

Question

So I have been working on a program that calculates nearest and larger 3rd power to a number which is entered (if entered number is 20 then result is 27 because 3^3=27). However due to my lack of skills I have stumbled upon a problem. It seems that variable result is used but never assigned (even if its value is asigned to it in a for cycle) Here is the code:

namespace ConsoleApp6
{
class Program
{
    static void Main(string[] args)
    {
        Console.Write("Enter a number: ");
        int num = Convert.ToInt32(Console.ReadLine());
        int result;
        for(int i = num; (i * i * i) >= 0; i--)
        {
            result = i * i * i;
        }
        Console.WriteLine("Nest 3rd pow. is: " + result);
        Console.WriteLine("Press any key to contiunue...");
        Console.ReadLine();
    }
 }
}

Thank you for your answers.

Answer 1

The comments have probably dealt with your issue (you didn't set a value for result when you created it, the compiler can foresee a scenario where no loop runs and there is never any assignment, but you always use it. A "use of unassigned local variable" error arises), but I wanted to point out that your program is some way off solving the advertised problem of finding the next larger int cube than the entered number

To solve this, cube root the entered number, round it up to the next integer and cube it

Math.Pow(Math.Ceiling(Math.Pow(num, 1.0/3.0)), 3.0);

As things stand, I'm not really sure what you're aiming to achieve with the loop, and it looks like it will run however many times needed to set the result to 0 (it loops until i is zero, result is 0). Perhaps you intended to start i from 2 and increment i until result was larger than num, but that seems less efficient than doing the calc directly

Answer 2

One overall rule of good programming praxis is to initialize a variable on the declaration.

The compiler error says that you are using result when it has not been assigned. That's because in your for loop you can't predict that it will iterate at least one time (therefore there are scenarios where the variable is used without ever being assigned).

As have been mentioned before, this can be fixed by initializing the variable (0 is the standard)

int result = 0;