To pass two parameters, you separate them with a comma, just as you do when you declare the method:
string n=Calculator.WriteNumber(53, 28);
If you want to pass an operator, then I'd do it with an enum:
public enum Operators
{
Plus,
Minus,
Times,
DivideBy,
}
Then:
public static string Calculate(int a, Operators op, int b)
{
int result;
switch (op)
{
case Operators.Plus: result = a + b; break;
case Operators.Minus: result = a - b; break;
case Operators.Times: result = a * b; break;
case Operators.DivideBy: result = a / b; break;
default: throw new ArgumentException("Unknown Operator: " + op);
}
return result.ToString();
}
You then call it like this:
string n = Calculator.Calculate(53, Operators.Plus, 28);
Note that I changed the name of your method: don't call something "WriteNumber" unless it actually writes something!