c# How to pass a variable from method into main?

Question

I am learning c#, I am creating a program that asks for user's first name, if the first letter is not capitalised the program will automatically capitalise it, I wanted to put this into a method but am having trouble with returning the value from the method into the Main method.

Here is the code I am trying

using System;
using System.Text;

namespace ConsoleApp1
{
    class Program
    {

        //Method for letter capitalisation 
        static string capitalise(string userName, char letter) { //users name, letter being replaced
            letter = char.ToUpper(letter); //capitalise first letter
            StringBuilder sb1 = new StringBuilder(userName);
            sb1.Remove(0, 1); //removes first letter
            sb1.Insert(0, letter); //inserts first letter from letter object
            userName = sb1.ToString(); //writes string builder into string
            return userName; //returns method value to the object
        }
        static void Main(string[] args)
        {
            string firstName;
            string lastName;

            Console.WriteLine("What is your First Name?");
            firstName = Console.ReadLine();
            Console.WriteLine("What is your Last Name?");
            lastName = Console.ReadLine();

            char capitalFirst = firstName[0]; // writes first letter of the name as a char
            if (char.IsLower(capitalFirst)) { //checks if char is lowercase 
                capitalise(firstName, capitalFirst); //calls for method and writes parameters
                firstName = capitalise(userName); // <--- here i am trying to write the user first name as a result from the capitalise method

            }

            //Same for last name...

            Console.WriteLine(firstName + " " + lastName);

}

The Error: The name username does not exist in the current context

Answer 1

It seems you may be being confused by some basic programming semantics, so I'll try to break this down for you.

• For one, you don't "pass" values from methods to the Main function of a program. You return values (hence the return statement)

  You pass parameters to methods and functions (for example: Test(1,2,3);, I've passed the ints 1, 2 and 3 to the method Test). I bring this up because I believe that you may be under the impression that you are modifying the scope/variables in Main by calling capitalise, which is not (and should not) be the case.

• Second, you need to understand scope, variables only exist in the scope within which they are declared; scope is more complex than this, but simply put, you can think of anything within curly brances ({ these }) as being a new scope; the only things that exist in that new scope are the things that exist above that scope and inside of it.

  Your Main method and the capitalise method have two different scopes, you cannot use userName in the Main method because userName only exists in capitalise.

So, the solution would be to update your Main method like so:

        static void Main(string[] args)
        {
            string firstName;
            string lastName;

            Console.WriteLine("What is your First Name?");
            firstName = Console.ReadLine();
            Console.WriteLine("What is your Last Name?");
            lastName = Console.ReadLine();

            char capitalFirst = firstName[0]; // writes first letter of the name as a char
            char capitalLast = lastName[0];
            if (char.IsLower(capitalFirst) || char.IsLower(capitalLast)) { //checks if char is lowercase 
                firstName = capitalise(firstName, capitalFirst);
                lastName = capitalise(lastName, capitalLast); 

            }

            //Same for last name...

            Console.WriteLine(firstName + " " + lastName);
        }

Answer 2

You can replace capitalize function for ToTitleCase:

        TextInfo textInfo = Thread.CurrentThread.CurrentCulture.TextInfo;

        string resultStr = textInfo.ToTitleCase("firstname secondname");

Result of resultStr variable is = "Firstname Secondname"

Answer 3

Because you don't have any variable with name "userName" in Main. You need take return of capitalise and then put in some variable. For example:

string userName = capitalise(firstName, capitalFirst); //calls for method and writes parameters
firstName = capitalise(userName); // <--- here i am trying to write the user first name as a result from the capitalise method

Answer 4

You're really overthinking this.

As the other answers and comments mentioned, yours is a problem of variable scope. In this case, "scope" refers to the block of code where a variable is declared and is therefore accessible.

Any variable declared inside of a brace pair ({, }) is only accessible inside of that pair. This area is referred to as a block. Method parameters - like username and letter in your example, are only accessible within the body of the method, conveniently also delimited by braces.

For instance, this is valid:

{
  string s;
  s = "blah;
  Console.WriteLine(s);
}

while this is not

{
    string s;
    s = "blah"
}
Console.WriteLine(s); // s has gone out of scope and does not exist here.

In your sample, there are a number of issues. You're calling capitalise in two different ways, one of which - with only one parameter, while the method expects two - is invalid. But, the immediate problem is this:

firstName = capitalise(userName);

userName is invalid here because it is an argument of capitalize. Main knows nothing of that userName, because it is declared in a different scope.

You might have meant:

firstName = capitalise(firstName, capitalFirst);

Complete working sample below. Use of StringBuilder is overkill and unnecessary in this case. StringBuilder is typically used when you need to build very large strings by concatenating a bunch of stuff. String concatenation requires some allocation and copying and potentially triggers the garbage collector, which can be a significant performance hit, and can consume tons of memory in extreme circumstances.

Good luck!

using System;

public class Program
{

    public static string Capitalize(string s)
    {
        if(string.IsNullOrEmpty(s))
            return string.Empty;

        string result = char.ToUpper(s[0]) + s.Substring(1);

        return result;
    }

    public static void Main()
    {
            string firstName;
            string lastName;

            Console.WriteLine("What is your First Name?");
            firstName = Console.ReadLine();
            Console.WriteLine("What is your Last Name?");
            lastName = Console.ReadLine();

            firstName = Capitalize(firstName);
            lastName = Capitalize(lastName);
            Console.Write("Hello, {0} {1}.", firstName, lastName);
    }
}