Implement a recursive program that displays all combinations of operators to reach a given sum

• I have to write a program that displays all the combinations of operators( + and -), to put between numbers from 1 to N (N>=2), in order to reach a targeted value X. It should write "N/A" if there is no possibility.

> For the input:

• n=6
• x=3

> It displays:

• 1 + 2 + 3 - 4 - 5 + 6 = 3
• 1 + 2 - 3 + 4 + 5 - 6 = 3
• 1 - 2 - 3 - 4 + 5 + 6 = 3

using System;

namespace ConsoleApp1
{
    class Program
    {
       static bool counter;

       static void Generate(int n, int x, int currentIndex, int result, string expression)
        {
            counter = true;

            if (currentIndex == n + 1)
            {
                if (result == x)
                {
                    Console.WriteLine(expression + " = " + x);
                }

                return;
            }

            Generate(n, x, currentIndex + 1, result + currentIndex, expression + " + " + currentIndex);
            Generate(n, x, currentIndex + 1, result - currentIndex, expression + " - " + currentIndex);
        }

       static void Main()
        {
            int n = Convert.ToInt32(Console.ReadLine());
            int x = Convert.ToInt32(Console.ReadLine());
            const int doi = 2;

            Generate(n, x, doi, 1, "1");

            if (!counter)
            {
                Console.WriteLine("N/A");
            }

            Console.ReadLine();
        }
    }
}

> It gives me the error : JRM003 (Error) : Don't use static fields. (line: 7, character: 7).
> Where can I place the "counter" in order to track if there is possibility of reaching to the targeted value, and get rid of the error.

Here's how I'd do it. Count in binary treating 0 as subtraction and 1 as addition:

    public static void Main(string[] args)
    {
        int n, x;
        String response1, response2;

        Console.Write("Enter a value for 'n' [n>=2]: ");
        response1 = Console.ReadLine();
        Console.Write("Enter a value for 'x': ");
        response2 = Console.ReadLine();

        if (int.TryParse(response1, out n) && int.TryParse(response2, out x))
        {
            if (n >= 2)
            {
                List<String> solutions = new List<string>();
                int[] numbers = Enumerable.Range(1, n).ToArray();
                int width = numbers.Length - 1;
                int max = (int)Math.Pow(2, numbers.Length - 1);
                for(int i=0; i < max; i++)
                {
                    int sum = numbers[0];
                    String binary = Convert.ToString(i, 2).PadLeft(width, '0');
                    String equation = numbers[0].ToString();
                    for(int d=0; d<binary.Length; d++)
                    {
                        char operation = binary[d];
                        equation = equation + ((operation == '0') ? " - " : " + ") + numbers[d + 1];
                        sum = sum + ((operation == '0') ? -1 : 1) * numbers[d + 1];
                    }
                    equation = equation + " = " + sum;
                    if (sum == x)
                    {
                        solutions.Add(equation);
                    }
                }
                if (solutions.Count == 0)
                {
                    Console.WriteLine("N/A");
                }
                else
                {
                    foreach(String solution in solutions)
                    {
                        Console.WriteLine(solution);
                    }
                }
            }
            else
            {
                Console.WriteLine("'n' must be greater than or equal to 2.");
            }
        }
        else
        {
            Console.WriteLine("Invalid value for 'n' or 'x'!");
        }

        Console.WriteLine("Press Enter to Quit.");
        Console.ReadLine();
    }

Output:

Enter a value for 'n' [n>=2]: 6
Enter a value for 'x': 3
1 - 2 - 3 - 4 + 5 + 6 = 3
1 + 2 - 3 + 4 + 5 - 6 = 3
1 + 2 + 3 - 4 - 5 + 6 = 3
Press Enter to Quit.