无法声明局部变量名称'choice'，因为它会给'choice'赋予不同的含义

Question

Sorry, I'm completely new to the programming world. I'm creating a console application that basically takes your input on whether you want to convert Celsius to Fahrenheit or vice-versa.

The problem I'm running into is:

"Error 3 A local variable named 'choice' cannot be declared in this scope because it would give a different meaning to 'choice', which is already used in a 'parent or current' scope to denote something else"

I tried looking at other examples, but they were far more complicated than my brain can understand for now.

namespace TemperatureApp
{
    class Program
    {
        static void Main(string[] args)
        {
            int choice;

            do
            {
                Console.WriteLine("Hi! This is a temperatue app");
                Console.WriteLine("Press 1 for C to F or 2 for F to C");
                //take the user input
                int choice = Convert.ToInt32(Console.ReadLine());


                if (choice == 1)
                {
                    Console.WriteLine("Great, you chose C to F. Now enter the temp.");
                    int celcius = Convert.ToInt32(Console.ReadLine());
                    //next line use the formula and show answer
                }
                if (choice == 2)
                {
                    Console.WriteLine("Great, you chose F to C. Now enter the temp.");
                    int fahrenheit = Convert.ToInt32(Console.ReadLine());
                    //next line use the formula and show answer
                }
                else
                    Console.WriteLine("That is not the right choice.");
                    //In this way, keep asking the person for either 1 or two

            }
            while (choice != 1 || choice != 2);

            Console.ReadLine();
        }
    }
}

Answer 1

int choice = Convert.ToInt32(Console.ReadLine());

should read

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

By putting the int in the second time, you are declaring another variable called "choice" inside the {}. That definition is conflicting with the one just outside.

Answer 2

It's all in the error message, you have declared your choice variable twice within the same scope.

When you read the value from the console input you don't need to re-declare the variable you just need set it. To elaborate:

int choice; // declare variable

do
{
    int choice = ...; // re-declare variable
}

On the second line you want to assign the variable a value, not re-declare it, to do that you just need to replace this line:

int choice = ...

With

choice = ...

Answer 3

The problem I'm running into is:

"A local variable named 'choice' cannot be declared in this scope because it would give a different meaning to 'choice', which is already used in a 'parent or current' scope to denote something else".

I tried looking at other examples

You shouldn't look at examples, but at the error and your code. The C# compiler is quite user-friendly with its messages, and this one is quite clear also. You just have to understand the language used.

A local variable named 'choice' cannot be declared

You declare a variable like this: variable-type variable-name , which happens on the line of the error, within your do -loop:

int choice = Convert.ToInt32(Console.ReadLine());

Here with int you declare the variable, int being its type. Removing int will make that line an assignment , which is what you need. The result of Convert.ToInt32(Console.ReadLine()) is assigned (=) to the choice -variable. You can only assign a variable after declaring it, but you have already done that earlier in the code. So the error says:

because it would give a different meaning to 'choice', which is already used in a 'parent or current' scope to denote something else

And if you look up in your code, you see that in a parent scope (in static void Main() ) a variable with the same name is declared:

int choice;

Now you should know you only need to declare a variable once, and that this is usually, preferably done in a scope as small as possible. In your case, you can simply remove the int before int choice = Convert.ToInt32(Console.ReadLine()); , because you also need to access choice outside the do -loop.

Answer 4

Try taking the choice variable declaration out of your cycle scope. Like this:

   int choice;

   do
    {
        Console.WriteLine("Hi! This is a temperatue app");
        Console.WriteLine("Press 1 for C to F or 2 for F to C");
        //take the user input
        choice = Convert.ToInt32(Console.ReadLine());


        if (choice == 1)
        {
            Console.WriteLine("Great, you chose C to F. Now enter the temp.");
            int celcius = Convert.ToInt32(Console.ReadLine());
            //next line use the formula and show answer
        }
        if (choice == 2)
        {
            Console.WriteLine("Great, you chose F to C. Now enter the temp.");
            int fahrenheit = Convert.ToInt32(Console.ReadLine());
            //next line use the formula and show answer
        }
        else
            Console.WriteLine("That is not the right choice.");
            //In this way, keep asking the person for either 1 or two

    }
    while (choice != 1 || choice != 2);

    Console.ReadLine();
}

}

Answer 5

You can't have a local variable named the same name as another local variable. You can have a local variable with the same name as a variable of a larger, non-local scope (class member for instance) but in that case the local variable hides the larger-scoped variable.

What you want to do is take the int off the second choice . You don't need to re-declare it, you just want to assign it.

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