using System;
namespace CsharpFundamentals
{
public class Person
{
public string FirstName;
public string LastName;
public void Introduce()
{
Console.WriteLine("My name is " + FirstName+" " + LastName);
}
}
class Program
{
static void Main(string[] args)
{
Person Aladdin = new Person();
Aladdin.FirstName = "ash";
Aladdin.LastName = "ketchum";
Aladdin.Introduce();
public class Person
{
public string FirstName; // like char FirstName[256];
public string LastName; // like char LastName[256];
public void Introduce() // this is a member function - structs can't do this
{
Console.WriteLine("My name is " + FirstName+" " + LastName);
}
}
Well by default class variables can only be used by the functions in the class. This may seem a slightly strange thing to do, but it's actually a very important feature of classes.
using System;
namespace CsharpFundamentals
{
public class Person
{
int age;
public void SetAge(int a)
{
if (a > 0)
age = a;
}
}
class Program
{
static void Main(string[] args)
{
Person Aladdin = new Person();
Aladdin.age = -99;
}
}
}
The reason for this is that if the variables are accessible then other code can set them to silly values e.g. my code tries to set the age to -99 and that's silly.
By making the variables inaccessible we force any code using the class to use functions provided by the class to set the variables e.g. like this:
using System;
namespace CsharpFundamentals
{
public class Person
{
int age;
public void SetAge(int a)
{
if (a > 0)
age = a;
else
Console.WriteLine("Invalid age {0}", a);
}
}
class Program
{
static void Main(string[] args)
{
Person Aladdin = new Person();
Aladdin.SetAge(-99);
}
}
}
Note that we still use public when defining the function SetAge.
That's because if we left off the SetAge function it couldn't be used outside the class either. It can often be useful to hide class functions so they can't be used outside the class.
Are you happy you understand what public means now?
Let me use an example. I'll modify the code to show this:
using System;
namespace CsharpFundamentals
{
public class Person
{
int age;
public void SetAge(int a)
{
if (a > 0)
SetAgeSub(a);
else
Console.WriteLine("Invalid age {0}", a);
}
void SetAgeSub(int a)
{
age = a;
}
}
class Program
{
static void Main(string[] args)
{
Person Aladdin = new Person();
Aladdin.SetAgeSub(-99); // NOT allowed!
Aladdin.SetAge(-99); // Allowed but silly
Aladdin.SetAge(18); // Allowed
But suppose our class has a maximum age i.e. you can't set the age to a value higher than this maximum. This could be useful so the SetAge function can check for silly ages like 1001.
It would be nice for code using the class to be able to get this maximum age e.g. so it can check it doesn't pass ages larger than the maximum to SetAge.
But this maximum age isn't a property of any particular object. It applies to all Person objects. Its the sort of thing that in C you would do with a #define. Yes?
using System;
namespace CsharpFundamentals
{
public class Person
{
const int MAX_AGE = 130;
int age;
static public int GetMaxAge()
{
return MAX_AGE;
}
public void SetAge(int a)
{
if (a > 0)
SetAgeSub(a);
else
Console.WriteLine("Invalid age {0}", a);
}
void SetAgeSub(int a)
{
age = a;
}
}
class Program
{
static void Main(string[] args)
{
int max_age = Person.GetMaxAge();
Console.WriteLine("Max age = {0}", max_age);
Yes. It doesn't matter if any Person objects have been created, or how many Person objects have been created. The static functions, and any static variables, always exist.
I tried to create public void Main() in C#; it says no static void Main found.
What exactly does it mean for Main to be static? I know the code works fine for public static void Main().
But why does Main have to be static?
I tried to create public void Main() in C#; it says no static void Main found.
What exactly does it mean for Main to be static? I know the code works fine for public static void Main().
But why does Main have to be static?
