C#

public interface IOperator
{
    double Operate(double leftOperand, double rightOperand);
}

public static class OperatorBuilder
{

    public IOperator BuildFromToken(string operatorToken)
    {

        switch (operatorToken)
        {
            case "*":
                return new MultiplyOperator();
        }

    }

}

public class MultiplyOperator : IOperator
{
    public double Operate(double leftOperand, double rightOperand)
    {
        return leftOperand * rightOperand;
    }
}

// example usage
public void Main(string[] args)
{

    // program is run like:
    // CalculatorExample.exe 5.0 6.0 *

    var operator = OperatorBuilder.BuildFromToken(args[2]);
    
    Console.WriteLine(
        operator.Operate(
            double.Parse(args[0]), 
            double.Parse(args[1])
        )
        .ToString()
    );

    // should return 30.0

}

• OperatorBuilder - responsible for identifying tokens and returning the correct type of operator
• MultiplyOperator, AdditionOperator etc. - responsible for performing an operation on some operands
• Your processing code - the code you already have is doing the scanning part, which is separate (IMHO) from the semantic understanding of the text you are reading

// syntax is dubious
delegate double OperateDelegate(double left, double right);

var operatorLookup = new Dictionary<string, OperateDelegate>();

operatorLookup.Add("*", ((left, right) => left * right));
operatorLoojup.Add("+", ((left, right) => left + right));

// etc.
// OR you could go even MORE terse!

var operatorLookup = new Dictionary<string, OperateDelegate>
{
    { "*", ((left, right) => left * right) },
    { "+", ((left, right) => left + right) }
};

// etc.

Shivamkalra wrote:

reading articles on code project

        [+ node]
       /        \
  [+ node]       D
 /        \
A       [* node]
       /        \
      B          C

ManagementObject processor = new ManagementObject("Win32_PerfFormattedData_PerfOS_Processor.Name='_Total'");
processor.Get();
ulong value = (ulong)processor.Properties["PercentProcessorTime"].Value;