Error when calling a function in C# because variable is used in parameter

Question

I'm new to c#, but I'm trying to create a basic program that can use a function that adds to numbers (this is just practice I know it's inefficient.

        {
            int AddNumbers(int num1, int num2) //Here's where the error comes
            {
                int result = num1 + num2;
                return result;
            }

            int num1 = 10;

            int num2 = 20;

            AddNumbers(num1, num2);

However, when I try it, it says that "A local parameter named 'num1' cannot be declared in this scope because that name is used in an enclosing local scope to define a local or parameter". I assume that this is because I declared the variables while calling the function, but I don't know how to fix it.

Thanks for any help!

EDIT: Just to be clear, the numbers after the functions are the number I would like to be added in the function

Answer 1

Local methods have access to every thing in the parent block. That is why you cannot define the same variable name more than once. Try this instead.

{
    int num1;
    int num2;

    int AddNumbers(int left, int right) => left + right;

    AddNumbers(num1, num2);
}

There is a guide for this as well found here: https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/local-functions

Answer 2

I guess you were trying to make a method for add Numbers. If you want to make a method, you need make method OUTSIDE of the Main code.

public static int AddNumbers(int num1, int num2)
{
    int sum;
    sum = num1 + num2;
    return sum;
}
static void Main(string[] args)
{
    int a = 10;
    int b = 20;
    Console.WriteLine($"a = {a}, b = {b}");
//First way to control the string: put $ infront of the string, and write code in the {})
    Console.WriteLine("a + b = {0}", AddNumbers(a, b));
//Second way to control the string: put {} and number (start with 0) and write code after comma
}

If you write as this, you will get an answer as

a = 10, b = 20
a + b = 30

For public static int AddNumbers(int num1, int num2) You don't have to think about public static yet. At the position of int, you can put another variables such as string, long, double. For that case, you have to return (various you put); at the end. If you put void, you don't have to put return and the thing you wanted will be done in the method.

Answer 3

Welcome to SO.

as you know you cannot have same variable name used in a method here is what you need

     {
        int AddNumbers(int num1, int num2) //Here's where the error comes
        {
            int result = num1 + num2;
            return result;
        }

        int num2 = 10;

        int num3 = 20;

        AddNumbers(num2, num3);

    }

you can have something like this:

class Program
{
    int p = 0;
  public  static void Main(string[] args)
    {
        int num1 = 10;
        int num2 = 20;           
     int num =  Method1(num1,num2);
     Console.WriteLine(num);
    }

    public static int Method1(int num1, int num2)
    {
        p = num1 + num2;
        return p;
    }      
}