Name: 程式語言（Learn Python For Beginners 2021 | Tutorial Part #2 | If Statements）
Uploaded: 2021-02-18T11:24:44.000Z
Duration: 10 min 41 s
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if that is the question hi today we're going to  be looking at if-else conditional statements in  

過去簡單式

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

現在進行式

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 print i  is 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 no i  is 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 an f  string 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

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 maybe i  should 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