1 00:00:04,790 --> 00:00:09,559 So this was an easy challenge - probably easier than some of the previous ones. 2 00:00:09,559 --> 00:00:13,400 We set it because we wanted to emphasize something that may not be obvious. 3 00:00:13,400 --> 00:00:17,720 If it's not obvious, it won't cause you a problem in your code, but it may confuse 4 00:00:17,720 --> 00:00:21,320 you when you read someone else's code. I'm going to start by writing my 5 00:00:21,320 --> 00:00:27,199 solution in the obvious way. We're gonna down here to line eight. We're going to 6 00:00:27,199 --> 00:00:34,100 add an else, colon. On the next line, print parentheses double quotes, using a 7 00:00:34,100 --> 00:00:43,039 replacement field with 0 in it, is not a valid number, closing double quotes dot 8 00:00:43,039 --> 00:00:49,789 format temp. Again, making sure we're keeping two blank lines between the end of 9 00:00:49,789 --> 00:00:54,109 the function, and the code starting on line 13. So if the input is a valid 10 00:00:54,109 --> 00:00:58,180 number, our function returns - you can see that's doing that on line eight. 11 00:00:58,180 --> 00:01:02,740 The obvious way to solve the challenge is to add an else block, which I've done. 12 00:01:02,740 --> 00:01:07,480 If they enter something that can't be converted to an int, we print the message. 13 00:01:07,480 --> 00:01:11,960 That code's fine - it works and many programmers would write it that way. 14 00:01:11,960 --> 00:01:17,240 What may not have been obvious, is that the else isn't needed. If the return on line 15 00:01:17,240 --> 00:01:21,530 eight is executed, then any code after that line won't be. The function will 16 00:01:21,530 --> 00:01:26,240 terminate at that point, and return to the calling code. So that means that some 17 00:01:26,240 --> 00:01:30,650 programmers won't use the else. Instead what they'll do is something like this, so 18 00:01:30,650 --> 00:01:33,490 I'll comment out the else. 19 00:01:33,630 --> 00:01:39,450 I'm gonna move the indentation back to the same level as the if. So the print on 20 00:01:39,450 --> 00:01:43,619 line 10 is indented one level back - it's not part of the if block as such, as it 21 00:01:43,619 --> 00:01:48,240 was before the else. And this will do exactly the same thing. If a valid number 22 00:01:48,240 --> 00:01:53,320 is entered, the function will return. If the user enters something that isn't valid, 23 00:01:53,320 --> 00:01:57,620 we get the message printed. To be clear, we only get to line 10 if 24 00:01:57,630 --> 00:02:01,979 invalid input is entered. So I run the program, which I'll do now and make sure that 25 00:02:01,979 --> 00:02:06,440 that does work. I'm gonna enter some random characters. 26 00:02:06,440 --> 00:02:11,460 We get the message - the random characters I typed is not a valid number. Pressing 27 00:02:11,460 --> 00:02:17,520 enter as I do now, without entering anything, comes back and says it's not a valid number. 28 00:02:17,520 --> 00:02:22,740 When I enter 500, the function returns the value 500 and we don't get 29 00:02:22,740 --> 00:02:27,069 the message. I'll finish with zero to terminate the program. 30 00:02:27,069 --> 00:02:32,320 So you will find code written that way, rather than using the else clause. 31 00:02:32,320 --> 00:02:36,720 So what I'm going to do is take a copy of this code. Well actually, I'll go back to the 32 00:02:36,720 --> 00:02:41,680 project pane, because I want to show you a comparison of both sets of code. 33 00:02:41,680 --> 00:02:44,360 So we'll copy this. 34 00:02:44,560 --> 00:02:50,000 We'll paste it and I'll call the second one guessing game else. 35 00:02:50,160 --> 00:02:54,860 With the else code what I'll do, with that version of the file, we're going to leave the else in 36 00:02:54,860 --> 00:03:00,180 and do the indentation. So we've got both versions now - we've got the else version, 37 00:03:00,180 --> 00:03:04,680 and also the version that we just worked on and ran, that hasn't got the else. 38 00:03:04,680 --> 00:03:11,060 Now if we now come up to Window, select Editor Tabs and split vertically, 39 00:03:15,069 --> 00:03:19,269 I should be able to close these other windows down now, and we can see both 40 00:03:19,269 --> 00:03:22,109 versions of the code. 41 00:03:23,240 --> 00:03:29,060 You can see there that the comparison, the left version, is the else version, 42 00:03:29,060 --> 00:03:32,760 and that's got the else clause in, and the file on the right hand side has got 43 00:03:32,760 --> 00:03:37,020 the else commented out, and the indentation level of the print is at the 44 00:03:37,020 --> 00:03:42,060 same level as the if statement. So whichever style you prefer is up to you. 45 00:03:42,060 --> 00:03:45,660 Else is unnecessary, but you may feel that it makes the code easier to 46 00:03:45,660 --> 00:03:48,390 understand. There's no difference in performance - 47 00:03:48,390 --> 00:03:53,700 they both compile to almost identical bytecode. Make sure you do understand the 48 00:03:53,700 --> 00:03:58,620 flow of execution here. The return on line eight will prevent any further code 49 00:03:58,620 --> 00:04:02,520 from executing. If you want to use the debugger to check, then set a breakpoint 50 00:04:02,520 --> 00:04:05,580 on line seven. You can then experiment with valid and 51 00:04:05,580 --> 00:04:09,340 invalid numbers, to verify that both these approaches will do the same thing. 52 00:04:09,340 --> 00:04:13,000 When you're happy that both ways of writing this do exactly the same thing, 53 00:04:13,000 --> 00:04:16,240 I'll see you in the next video.