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‫Earlier we discussed how to use the command line arguments.

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‫And this part you will learn how to handle user input and make a program that does basic operations.

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‫We will also see how to display a basic manual to the user explaining how our program works and what

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‫are its requirements.

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‫This is necessary since our application doesn't use console line to ask the user for input.

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‫Instead, all the data that our app needs will be provided at the start using the command line arguments.

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‫So what we can do is we can say something like provide arguments next time, pass help if you want to

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‫get more details, for example.

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‫Okay.

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‫So this would be then the statement that the user sees once he starts the application.

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‫And now let's actually check if the user entered help.

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‫So if he entered help, we are going to give him some help.

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‫We're going to say instructions.

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‫Use one of the following commands followed by two numbers.

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‫Use add to add two numbers.

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‫Sub two subtract two numbers.

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‫Our application will then pause and return.

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‫So now let's actually handle the user input because rule number one, never trust the user because the

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‫user will make mistakes.

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‫And it's our job to make our application handle all of these possible input mistakes that the user might

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‫provide.

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‫So first, our application needs three arguments to do its job so it's safe to quit the application

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‫if either more or less than three arguments were provided, since we need exactly to so we could do

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‫something like this here.

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‫If our length is not equal three then write invalid arguments.

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‫Please use the help command for instructions and read the key.

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‫So now, since we made sure that we won't go any further in our app unless we have three arguments,

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‫let's check if the format of arguments is correct, since our arguments will be in the format of a command

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‫followed by two numbers.

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‫We want to check if the two numbers are in a correct format and we do that by using the float.

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‫Try parse functionality so which takes a string that it will try to pass into float and a float variable

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‫that it will use to save the parsed data if the parsing operation was successful.

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‫Therefore, we're going to add this code here saying this number one parsed and this number two parsed.

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‫So basically we get those values right and we can now go ahead and now we can check if the user passed

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‫or entered something that is actually going to be a floating number or not.

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‫So now we can check if those two are true or not.

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‫So if they are not true.

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‫So both of them or either of them.

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‫So if either of them is false, then we can just say invalid arguments.

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‫Please use the help command for instructions and then read key and quit the application.

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‫So now at this point, we can go ahead and actually calculate the result using a float where we are

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‫going to store the results and then we can use a switch case statement like so where we take arcs at

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‫position zero as the switch statement.

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‫So we're comparing is it add.

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‫So if the user entered add, then we're going to use NUM one, which was this outflow number one.

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‫And number two.

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‫So we're going to add them together, store the result and result and write it onto the console.

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‫And at this point, break out of the switch case.

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‫And then if it was set so the user entered up as the first entry at ARX zero, then it will subtract

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‫NUM two from num one.

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‫And then it will display the results here.

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‫And finally, in the default case, if none of the two options add or sub were given, then it will

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‫say invalid arguments.

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‫Please use the help command for instructions.

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‫And they will break out of the case.

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‫So at this point, we can get rid of this bright line here that Ricky will be fine.

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‫And let's now run the application.

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‫And of course, in order to make it run, make sure that you first close your command prompt.

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‫Otherwise it won't work.

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‫So now it will be built.

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‫Now we can go ahead and pass arguments to it.

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‫So open the command prompt using CMD, so Windows Key and then CMD.

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‫And then you can drag your applications a file which you can of course find via solution explorer.

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‫Right click and here open folder and here go to bin debug.

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‫Dot net five in my case and here you will find the main args demo.

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‫So now you can drag this into your command prompt.

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‫So drag it in here and you can then enter for example, sub and five six.

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‫So it will say the sub of five and six is minus one.

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‫So let's do it again.

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‫Let's try it with a different entry.

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‫Let's use add 15 and 13 and you can see the sum of 15 and 13 is 28.

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‫And now let's enter something else, something stupid like so you can see invalid arguments.

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‫Please use help commands for instructions.

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‫Let's try that.

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‫Let's enter.

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‫Help.

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‫And we can see use one of the following commands followed by two numbers.

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‫Add to add two numbers sub to subtract two numbers.

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‫Okay, so let's try it again.

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‫And here let's use any random keyword and add two numbers and you can see that this will not work because

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‫the arguments weren't correct because it doesn't expect q w e it expects either add or sub.

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‫So.

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‫That's basically it.

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‫That's how we have actually built our first command line program using arguments from outside of the

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‫application.

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‫So user input directly in the command prompt.

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‫And now you could of course extend your application to do whatever you want with it, and it would do

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‫wonders for you.

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‫All right.

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‫So that's it for this video.

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‫I hope you enjoyed it.

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‫And you're now able to create your own little applications using the command prompt and actually using

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‫user input and know how to use the ARX.

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‫So how to use all of those beautiful main args that you have by default when starting the application.

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‫So see you in the next video.