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• if that is the question hi today we're going to  be looking at if-else conditional statements in

• python for lesson two in the series of getting  started with python so let's get straight to it

• hi guys i'm david and today we're doing  our second lesson in our course on how to

• get started in python and today we're going  to be looking at if statements with strings

• and integers so i guess the best idea is to  get to our computer and get started with it

• right this is the second lesson in the course  if you haven't done the first lesson on getting

• started with python i suggest you go to the  card above and click on that to do that first

• today we're going to be looking at if statements  so i've started a new folder and created a main.py

• just like in the first lesson and i guess we  should get started right as in the first lesson

• we're going to start with integers integers as you  know if you did the first lesson are a variable

• which is a number a number which can be any number  so we're going to start with i equals zero so what

• we actually want to do is ask python to print  out a statement on the screen if i equals zero or

• or if i equals one so let's get to that the good  thing about python is it's pretty plain english

• so let's go if i equals equals zero and then you  press the double dot to end the statement now what

• you're actually going to do now is press enter and  inside the visual studio they will automatically

• indent it everything that's indented will be part  of this if statement so we're going to write print

• we're going to do double quotes here and we're  going to write i is equal to zero then we're going

• to go down to a line and we're going to press  backspace and write else now else means that if i

• if i is not equal to zero we're going to print  something else out so we're going to press enter

• again and that's going to indent the text printis not equal to zero so then we're going to save

• that and we're going to run the script so what's  happening here is your python scripts checking

• to see if i is equal to zero if it is will print  out like in the last lessons so let's go python

• main dot p y and as you can see i is equal to zero  because we said i up here now if we work it out as

• one then press save and rerun it it will say  i is not equal to zero so the if statement is

• working perfectly well okay so let's clear that  and move on to something a bit more complicated so

• what happens if i is more than zero so it could be  any number that's above zero okay so let's go i i

• is greater than zero so i is greater than  zero let's save that and see if that works

• i is greater than zero of course it is because  it's one now what if we set this to zero

• and run again i is not greater than zero because  it is agile equal to zero so that works as well

• what about if i is equal to three nois greater than three so for this work

• i is not greater than three so  we're gonna offset i to four

• and that's working absolutely perfectly wonderful  right it's because i is four so it is greater than

• three it should say three here but anyway you  know what i mean right okay fantastic so okay so

• now you've done your first if statement i know  it was simple but that's the great thing about

• python everything's written in very much plain  english so it's understandable and easy to code

• let's go on to something a little more complex  and add an else if statement so that's going

• to give us another condition to our conditional  statement so let's give that a go okay so we're

• back here i've done and then we can add an else  f now to do an else if we have to type l sif

• i equals equals four and then we're going to  go here and we're going to do a print statement

• i is equal to four so now what we have is an if  statement saying that we have i is equal to three

• if it's not it may be equal to four and if it's  not it will print this so let's give this a go

• there you go i is equal to 4 which is great  that's wonderful you've now done your first

• conditional statement in python so let's have  a look at maybe adding some strings instead

• of an integer okay what happens if we decide to  make this into a string so this is a just string

• so if we go here and then we type this  and then run it we're going to clear the

• terminal down here and run it see what happens  you see it's not equal to zero which is perfectly

• great because it's a string now so how would we  do it if we wanted to return a string that only

• inc contained the word this in it okay the best  way to do this is to go back to our if statement

• here and modify it i'm going to comment all this  out now to comment out all you have to do is do

• this like this highlight all and  then do control and that will

• that will comment out all of the team now comments  you may not have seen before comments will put a

• hashtag in front of the statement which means  the computer will see them but will not run them

• so it's very useful if you're adding tank for  another developer or reminder to yourself of

• what an actual function does so right  here we could write this is a function

• for if string okay now we can get on and we  will know next time here that we come here

• anything below this line will work with anstring right okay okay to do this what we're

• going to do is we're going to create another  string which is going to be the found string

• okay found string is going to be the words that  we're going to be searching for this is okay so if

• found in i we're going to type print

• i found

• do and then if not we're going to  do else and then else we'll print

• not found okay so the idea is is if  we find the text this is inside the i

• string we'll type out i found you and if not  we'll type not found okay so let's give it a go

• i found you so as expected python  actually found inside the string

• the text that we were looking for and then  printed out the statement that we wanted

• okay now we've done the simple strings  maybe we should look at some arrays

• an array is a list of strings or integers  all stocked into one variable so i guess

• that's the next idea okay let's have a look  at this then all right okay so array could be

• u equals and then we go over here in between  a square bracket so we're going to write apple

• and then here and then maybe  we should write windows

• and maybe what about doors okay maybeshould spill that quick okay so inside

• this one array we have several values okay  so how would we go about printing out these

• photos let's have a look at printing  them to the console if we go print

• you this is what you get back i'm going to comment  this out so we don't get the old comments here

• we're going to save okay let's print u to  see what happens okay as you can see we have

• the full array of all of the values in uh printed  out now what if i wanted just to print out apples

• so anything about arrays is that actually they  all start with zero so let's go and write u

• squared brackets zero and that will bring up  our first value which would be apple if we

• wanted pair it would be one if we wanted windows  it would be two try windows and go windows okay

• wonderful so now we have a look to the slide uh  now i've looked a little bit into arrays maybe

• we'd do an if statement with an array so how would  we go about doing an if statement for an array so

• we're going to do a found straight versus found  string again here and we're going to write apple

• much like this string above we're going to  try if found in you and i'm going to print out

• i found an apple and then we're going  to go down to next slide and right else

• all right statement which is going to be simply

• nothing here okay cool right now let's  have a look see whether that works

• we're gonna go brian and i found an  apple fantastic that's brilliant so it's

• actually gone through our array and found  an apple inside our array that's wonderful

• okay we've had a bit of a look into if statements  and how they work we even went into slightly

• deeper into an array and we also looked at  adding comments to our script to actually getting

• into python and how it works I hope you enjoyed  this lesson it's part of a series that I'm going

• to be doing out every day of the week so I'll  see you tomorrow if you like the video thanks

• for liking it and please don't forget to subscribe  for the next videos have a great day cheers bye

if that is the question hi today we're going to  be looking at if-else conditional statements in

A2 初級