One day while walking past Ritchie's room I overheard an interesting conversation. There was a woman's voice, and oddly, it sounded like she was exerting authority over Ritchie. I had only ever known Ritchie as the leader of the resistance, and it was hard to imagine who he would let talk to him in such a tone.

"You need to send ten more people to Wonderland." she said. 
"I can only spare nine. We can't keep sending you ten people every month. We don't have that many people!" Ritchie replied, almost begging.

"Ritchie, you know that everything we do is for the human race. We need people if we want 

 to succeed. This is our last hope to conquer the machines!" 
"I know, I know." Ritchie replied. "But I just don't have a tenth person for you. We're already running on a skeleton crew as it is."

"What about the one you pulled forward through time; Teo was his name, I think?" she asked. 
"He wouldn't do. He's learning very fast, but he's still a novice. If you ask him what something as simple as a 

 is he'll be in a state of complete mental stupor for an hour." Ritchie said. I know I'm not the best coder, but I personally thought his words were a bit harsh. 

"Let me be the judge of that." the woman replied, "I'll evaluate him tomorrow." 

Guessing that this was near the end of the conversation, I quickly hurried on my way. Receiving prior news of a surprise exam is never bad, but I was still confused as to who the woman was and what they were talking about. I'd have the answer to the former question within 24 hours, and it seemed like the answer to the latter, for better or worse, would depend on how I measured up to the woman's evaluation. 'Wonderland' and 'Project Rust' meant nothing to me, but I 

 want to prove to Ritchie that he was wrong about me. I'm smarter and had learned much more than just what he had taught me to this point. To prove it, I needed to learn those terms Ritchie had used: 

 . I decided to seek Tom out and see if he could give me a quick lesson.

Tom was happy to see me, and luckily, willing to teach me about 

 . I had been a little worried that these would be part of the codes that were reserved for the resistance group's leaders. 


"As you know, Teo," Tom started, "in C#, every variable and function return value has a type." 
"Yes," I said, "we need to specify a type such as 

 , or others." 
"Perfect. I see that you've learned some things after I saw you last time! Sometimes the type can be quite long. For example, to create a double array, your code would look like this." Tom said, opening his laptop.

For simplicity and less typing in C#, there's a special type replacement token, 

 is just a syntactical shortcut that forces the compiler to infer the specific type from your expression. 

The following code does the same as the first code shown above, but with much less repetition.

 , the compiler knows you're creating an array of doubles and automatically makes the type of the array itself match that of its values; in this case, 

It is very important to understand that using 

 of the code at all, it just changes how the code looks. 

Here are a few pairs of code examples that are written differently, but do the same thing:

"Are you following me, Teo?" Tom asked. 
"Yes," I answered, "but I have a question: can I replace 

 ?" 
"Yes, Teo. You can replace any type with 

 as long as the compiler can understand what type you mean. Here are some constraints for using 

 can only be used for local variables inside methods. 

 for a method's return type or a method's parameter type. 

The variable must be initialized with a value if it is declared with 

Is it considered good style to declare every local variable with 

" 
"That depends on your coding style. Some programmers prefer to use 

 for all possible local variable declarations. Others say that it should 

 be used for variables that hold a function return value. Finally, a small minority of programmers prefer to 

using it wherever you can to start, and when you're comfortable with it, re-evaluate. 

 where I can." 
"Good. Here are some excersises to get you more familiar with 

Learn how to apply var keyword in C# programming language at C# tutorial for absolute beginners.