RPG Variables vs C# Variables

In RPG we define variables in our 'D or C Specs.  We don't have to  uniquely declare character or numeric-  just the inclusion of a value in the decimal places column is enough. Leave it out and you just defined a character variable.
For the most part this is all you need to write 90% of business applications. There are other variable types such Binary, Graphic etc but these are encountered less often.
 

DName+++++++++++ETDsFrom+++To/L+++IDc.Keywords++

D NameofDog       S             24              
D Counter         S              2  0  
D  Price          S              5  2           
D Datefield       S               D             

Here's the equivalent in C#

String NameofDog;
int Counter;
decimal Price;
DateTime datefield;

The first thing that you will notice is that there is no length defined for the fields in C#. That's a great improvement over RPG where you usually explicitly declare length and end up in lots of trouble when a value gets chopped off when moved to a smaller field.

In C# there are way more value types than needed such as byte (for numbers 0-255), sbyte, short, long, float etc.





Common Value Types in C#


Int - integer - whole numbers (no decimals). Useful for counting.


string - holds alphanumeric values


bool - true or false (similar to indicators)


double any decimal up to 15 significant digits


decimal - any decimal up to 28 sig. digits

The variable declarations in RPG did not quite translate to C#. There is no Date value type in C#.  The statement ' DateTime datefield;' declares an object reference called datefield. How do I know this? Only because I know there is not value type of date in C#.  The fact that I am declaring an object called datefield just as I would a variable value brings up all sorts of interesting things about C# - mainly that objects are just another kind of variable. More on that later.

What about Operations on variables?


Let's add 1 to Counter in RPG and C#

RPG

Counter = Counter + 1;

C#

Counter = Counter + 1;

The code is the exact same in both!  There are other differences but we'll get operations in another post.




Lot's of free stuff inside


When you declare a variable in C# whether it is a value type like an integer or a 'reference' type like the DateTime object I created, along with the variable comes packaged  actions you might need on it.  In RPG if I want to convert my counter to a string variable, I would do the following.





RPG


Character = %char(Numeric); 



In C#, there is a method or function included in the variable when you declare it. The brackets indicate that ToString is a method.

Character = Numeric.ToString();

This is a fundamental and important aspect of C# - The actions you perform on variables and objects are often methods of that variable or object. If you want to trim the end of a string in C# you just say Character.Trim(); . Because you declared Character as a type String and String has all these methods now Character has them. There is no 'trim' opcode or expression. It's a method of string and when you declare a variable as a type string it gets all the methods belonging to string.

What's great about this is that you don't have to wait 10 years for IBM to come up with another op-code - you just write one yourself!  But, you may be asking, how do I know what method to use? There must be thousands. There are. However the Visual Studio IDE makes it simple and has a feature called intellisense - it fills out the statement as you type showing a drop down of all the methods and properties of an object or variable. Don't worry if this doesn't make a huge amount of sense right now. You'll get the hang of it with practice but it is one of those kind of mind-flips that is a big switch from Procedural RPG and Object Oriented C#.  It also makes sense. While RPG is an awesome language it has hit a stone wall. Creating lots of more opcodes or expressions is just going to make the language more complex. C# doesn't need lots of 'op-codes' - in fact there are about 77 in C# 2.0 and many you will never use. Most actions come from methods in classes.