C# Methods, Parameters, and Return Values

As programs grow, Main can become a long sequence in which input, calculations, validation, and output are tangled together. A method creates a boundary around one operation and gives it a name such as CalculateTotal or IsValidAge. The name lets the caller reason at a higher level without rereading every statement.

Calling CalculateTotal transfers control into that method. Its statements run, return sends a value back, and execution continues after the call. The method can be called many times with different arguments without copying its implementation.

In static decimal CalculateTotal(decimal price, int quantity), the final decimal before the name is the return type. The parameter list states that callers must provide a decimal followed by an int. Inside the method, price and quantity are local names for those supplied values.

A void method returns no value. It is appropriate for an action whose useful effect is elsewhere, such as printing a heading. Calculations are usually more reusable when they return data instead of printing it, because a caller can display, store, compare, or test the result.

static bool IsValidPercentage(decimal value)
{
  return value >= 0m && value <= 100m;
}

static void PrintDivider()
{
  Console.WriteLine("----------------");
}

A method that receives all needed values and returns a result is easy to understand and test. CalculateDiscount does not need to know whether the subtotal came from a console, file, or web request. It also does not decide how the result is displayed.

This separation is not a rule that every method must be mathematically pure. Some methods must read files or send messages. The point is to keep side effects intentional and avoid hiding unrelated work inside a name that sounds like a calculation.

using System;

class Program
{
  static decimal CalculateDiscount(decimal subtotal, bool isMember)
  {
      decimal rate = isMember ? 0.10m : 0m;
      return subtotal * rate;
  }

  static void Main()
  {
      decimal subtotal = 80m;
      decimal discount = CalculateDiscount(subtotal, true);
      Console.WriteLine($"Pay: {subtotal - discount:0.00}");
  }
}

Pay: 72.00

Pass the smallest meaningful inputs. A method that needs price and quantity should not accept five unrelated values ‘in case’ they become useful. A narrow contract makes dependencies visible and reduces the number of states to reason about.

Optional parameters provide a default, and named arguments identify values at the call site. They help when a parameter is genuinely optional or several arguments of the same type are easy to confuse. Too many optional switches often signal that one method is trying to perform several operations.