Given the following flags,

  [Flags]
    public enum Operations
    {
        add = 1,
        subtract = 2,
        multiply = 4,
        divide = 8,
        eval = 16,
    }

How could I implement an IF condition to perform each operation? In my attempt, the first condition is true for add, eval, which is correct. However the first condition is also true for subtract, eval, which is incorrect.

        public double Evaluate(double input)
    {
        if ((operation & (Operations.add & Operations.eval)) == (Operations.add & Operations.eval))
            currentResult += input;
        else if ((operation & (Operations.subtract & Operations.eval)) == (Operations.subtract & Operations.eval))
            currentResult -= input;
        else
            currentResult = input;

        operation = null;

        return currentResult;
    }

I cannot see what the problem is.