Difference between revisions of "PHP-and-MySQL/C2/Logical-Operators/English"
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Latest revision as of 18:39, 1 December 2012
| Time | Narration |
|---|---|
| 0:0 | Hello and welcome to a tutorial on "Logical Operators". Its a very brief tutorial but I will keep it like that at the moment. |
| 0:09 | I'll use an example of an "if" statement again because that's all I have got at the moment. |
| 0:18 | What is a logical operator? Let's add a bit of logic and say its the 'and' or the 'or' operator. |
| 0:27 | Now if I start creating my basic layout for my "if" statement i will get to work on showing you what you can do with these. |
| 0:43 | Before we had example such as 1 is greater than 1 which at the moment is going to return 'false' |
| 0:54 | let's just check it to see where we are.... right . So that's "false". |
| 1:02 | Now what if I said "if 1 is greater than 1 or 1 equals 1". |
| 1:18 | Now we don't write it as 'or' we write it as two horizontal lines or two pipes. |
| 1:27 | Not quiet sure about that but if know my keyboard it would next to the shift key - two horizontal lines and that means 'or'. |
| 1:38 | So if we compile this what do you think the result is gonna be? |
| 1:43 | Now let's run through this once - if 1 is greater than 1 - "false" and so we have written "false" or 1 is equal to 1... |
| 1:54 | We know that 1 equals to 1 is "true" so here we are saying 'or' 1 is equal to 1 not 'and' because if we said 'and' then both would have to be "true". |
| 2:04 | or either of these could be "true" to make this. |
| 2:07 | The output. So hopefully we will get "true". |
| 2:14 | Okay so that's the 'or'. |
| 2:17 | It basically allows you to take two comparisons, show them into your "if" statement and if either of them are "true" - so its like an "either" operator... |
| 2:29 | "either" of them are "true", you will be left with "true". |
| 2:35 | "and" operator is a different matter. |
| 2:39 | "and" requires both of these to be "true" for this to be executed. |
| 2:44 | So we have get "false" here because 1 is not greater than 1. |
| 2:51 | We go back to our comparison operators and we will say "if 1 is greater than or equal to 1 'and' 1 equal 1", here we will get "true". |
| 3:01 | So now, all I can really think about is to add a few variables in to test this. |
| 3:08 | But I am pretty sure that you have got the hang of variables by now, by following my other tutorials. |
| 3:12 | So these are the two logical operators. |
| 3:17 | You will find them very useful because you might want to say for example - this is a very classic example. You'll find it in one of my projects.... |
| 3:27 | It is a "login" form. Say a user wants to login to a website. |
| 3:34 | You've probably logged into a website before and it said to enter your "username" and "password". Now the keywords are in there. |
| 3:40 | We need to check if the users have entered the "username" and the "password". |
| 3:44 | If they haven't, there is no point in comparing the "username" to the "password". |
| 3:48 | So we can say, for example, "if username and password". |
| 3:52 | In fact let's do this. I'll say "username" is equal to "alex" and my password is equal to "abc". |
| 4:04 | Now I will substitute these. I can say "username" and "password". |
| 4:11 | At the moment, this will say "true". |
| 4:15 | I'll change this. I'll say 'ok' or 'you forgot to fill out a field' because there will eventually be HTML fields. |
| 4:27 | This is going to be okay because we have got both values. |
| 4:32 | So let's try it. Yes, that's saying "ok". |
| 4:37 | Now what happens if I forget to type my password in there? There's nothing in there at the moment - no space - lets get rid of that. |
| 4:45 | 'You forgot to fill out a field'. |
| 4:50 | So if you imagine these are coming from the user - so it's been submitted as you typed your "username" and "password" in. |
| 4:57 | We are saying "username" and "password"; basically "username" itself is "true" because it exists... |
| 5:03 | If you had that inside, that would be acceptable; that would be "true". |
| 5:14 | We'll just check that there you go. |
| 5:18 | So because we have got "username" and "password" then that's fine. |
| 5:23 | But for the 'or' that doesn't really makes sense and you can imagine what will happen. |
| 5:28 | So right now, this will equal "true" because we have got both values. So this is 'ok'. |
| 5:36 | Now if I go with both of them and try it out. |
| 5:42 | "if the username exists" so if the username is "true"... |
| 5:46 | At the moment there is no value - so its "false". |
| 5:48 | "or the password is true" - that is, the value exists; at the moment it doesn't, so it is "false". |
| 5:52 | So we are going to say "You forgot to fill out a field". |
| 5:56 | I'll just write here nothing because at the moment it means nothing. |
| 6:03 | So refresh and we get nothing. |
| 6:05 | So you see, already I have explained how useful these can be in so many every day php applications. |
| 6:13 | For example - a form someone can fill in. You will find many other users for it. |
| 6:16 | But that's it then. |
| 6:19 | Two operators that are logical operators. |
| 6:24 | Just try them out and see what all you can do with them. |
| 6:28 | I will be using these most definitely in one of my projects quite soon. |
| 6:30 | Thanks for watching. |
| 6:35 | This is Sidharth dubbing for the Spoken Tutorial project. |
