1 00:00:00,840 --> 00:00:05,540 In the last lecture, I said we'd make a routine that handles errors, so let's do that. 2 00:00:05,910 --> 00:00:12,330 What I'm going to do is come down here to my main function and create a new path and a new euro that 3 00:00:12,330 --> 00:00:12,840 I'm going to handle. 4 00:00:12,840 --> 00:00:14,100 And I'll call this divide. 5 00:00:15,240 --> 00:00:16,000 And up here. 6 00:00:16,620 --> 00:00:20,970 Of course, we need to point that to the correct function divide, which doesn't exist yet, but that's 7 00:00:20,970 --> 00:00:21,500 no problem. 8 00:00:21,510 --> 00:00:24,390 We can create one func divide. 9 00:00:25,110 --> 00:00:27,510 And because this is a handler, it has two parameters. 10 00:00:27,510 --> 00:00:36,630 The response writer W is KTP Dot response writer and a pointer to a request. 11 00:00:37,770 --> 00:00:39,000 And that's supposed to be a pointer. 12 00:00:39,000 --> 00:00:42,950 So let's make it a pointer and give her curly braces. 13 00:00:43,650 --> 00:00:46,890 And now here I want to call a function that does division. 14 00:00:46,890 --> 00:00:51,320 And the reason I'm doing division is that dividing by zero is generally a bad idea. 15 00:00:51,690 --> 00:00:53,070 So let's create another function. 16 00:00:53,190 --> 00:01:01,590 Func divide values that takes two parameters, X and Y, but this time I'm going to make them float's. 17 00:01:02,310 --> 00:01:06,180 I'll make it a float thirty two, which is another of the basic data types. 18 00:01:06,180 --> 00:01:09,840 So far we have seen strings, we have seen INTs and float. 19 00:01:09,840 --> 00:01:11,550 Thirty two is just a floating point number. 20 00:01:12,010 --> 00:01:16,890 I could have used float 64 if I wanted, but it doesn't matter because I'm going to just use this for 21 00:01:16,890 --> 00:01:17,640 a quick test. 22 00:01:18,870 --> 00:01:21,630 That function is going to return to things. 23 00:01:21,970 --> 00:01:26,760 It's going to return a float thirty two and it's going to return an error. 24 00:01:26,760 --> 00:01:28,870 And if there is no error, it should return nil. 25 00:01:29,280 --> 00:01:30,600 So how do we do this? 26 00:01:30,810 --> 00:01:37,200 First of all, well, the basic logic is going to be the result is assigned X divided by what? 27 00:01:38,160 --> 00:01:44,640 And I'll return Y and nil and that actually works just fine. 28 00:01:44,970 --> 00:01:45,780 I not return. 29 00:01:45,780 --> 00:01:48,380 Why return result and nil. 30 00:01:48,390 --> 00:01:49,380 And that works just fine. 31 00:01:49,620 --> 00:01:52,100 But there's no actual error generated here. 32 00:01:52,110 --> 00:01:57,740 So what I need to check is to make sure that Y is greater than or equal to zero. 33 00:01:57,840 --> 00:02:04,770 So all I have to do is say if Y is less than or equal to zero then I want to stop, I want to generate 34 00:02:04,770 --> 00:02:05,280 an error. 35 00:02:05,280 --> 00:02:11,040 And I can do that by saying error, which is a new variable, is assigned the value of and this is a 36 00:02:11,040 --> 00:02:18,870 built in function errors new and some strength cannot divide by zero. 37 00:02:19,230 --> 00:02:29,880 And at that point I want to return and I'll just say float thirty two I point zero and er so that's 38 00:02:29,880 --> 00:02:30,150 that. 39 00:02:30,510 --> 00:02:34,680 If this, if this function gets the wrong thing here, errors don't new. 40 00:02:35,380 --> 00:02:36,300 Let's try that again. 41 00:02:36,810 --> 00:02:40,130 Errors not new. 42 00:02:40,140 --> 00:02:40,640 There we are. 43 00:02:41,670 --> 00:02:43,190 It just had to import it up here. 44 00:02:43,200 --> 00:02:47,850 Errors return return to zero and the error. 45 00:02:47,850 --> 00:02:48,960 I don't care about the zero. 46 00:02:48,960 --> 00:02:51,780 It's the error that I'll be checking for up here and divide. 47 00:02:51,900 --> 00:02:53,160 I'm not doing anything yet. 48 00:02:53,160 --> 00:02:56,850 So let's actually call this function and I'm going to get two values from it. 49 00:02:56,850 --> 00:03:02,880 I'll get my float, which I'll call F and I'll get an error that will be nil if there is no error but 50 00:03:02,880 --> 00:03:05,040 will be not nil if it is an error. 51 00:03:05,520 --> 00:03:11,010 And that is I get those two values by calling the function I just created divide values and I'll put 52 00:03:11,010 --> 00:03:16,200 in one hundred and one hundred point zero because it's the float and ten point zero. 53 00:03:17,340 --> 00:03:20,490 If error is not equal to nil, then what do I do. 54 00:03:20,490 --> 00:03:23,190 I want to write to the screen so I can just use my standard. 55 00:03:24,800 --> 00:03:28,250 Format or format F, print F. 56 00:03:30,580 --> 00:03:38,590 You cannot divide by zero, and at that point, you think I could just stop because, you know, well, 57 00:03:38,590 --> 00:03:42,160 we've got the air, we've written the scream, let's leave it like that and show you why you can't do 58 00:03:42,160 --> 00:03:46,650 that if there is no air that I actually want to write the result to the screen. 59 00:03:46,690 --> 00:03:55,000 And I can do that by format F F, format s, print F. 60 00:03:56,980 --> 00:04:00,400 And what I'm going to put in is a string and it will be a float. 61 00:04:00,520 --> 00:04:10,930 So the placeholder for float is percent F divided by percent F is percent F and then I have to of course 62 00:04:10,930 --> 00:04:15,250 fill in my placeholders and those would be X, Y and F. 63 00:04:17,020 --> 00:04:17,480 All right. 64 00:04:17,770 --> 00:04:19,420 So what is wrong with this? 65 00:04:19,480 --> 00:04:21,480 We have got to put my response right here in front of it. 66 00:04:25,400 --> 00:04:27,770 Not enough for the wrong place for my place. 67 00:04:27,850 --> 00:04:28,640 Let's try that again. 68 00:04:28,940 --> 00:04:30,560 I think I need more caffeine once again. 69 00:04:32,230 --> 00:04:32,890 That's what I want. 70 00:04:33,200 --> 00:04:39,740 Now, if I run this and I'm going to right now, everything compiles undefined X and undefined Y, let's 71 00:04:39,740 --> 00:04:40,730 find X and Y. 72 00:04:43,010 --> 00:04:43,490 Oh, yes. 73 00:04:43,490 --> 00:04:46,940 I didn't actually have values for X and Y, so I'll just hard to lose. 74 00:04:46,940 --> 00:04:49,580 One hundred and ten. 75 00:04:51,630 --> 00:04:52,730 I'll try that again. 76 00:04:54,800 --> 00:04:55,990 Everything compiles. 77 00:04:56,000 --> 00:05:00,290 I go back to my web browser, I reload the page for the home page that works great. 78 00:05:00,620 --> 00:05:08,930 I go to the about page that does what I want and then I go to the divide page and one hundred divided 79 00:05:08,930 --> 00:05:11,190 by ten is ten and that's correct. 80 00:05:11,240 --> 00:05:14,660 OK, let's go back here and let's try to divide by zero. 81 00:05:15,260 --> 00:05:22,520 So I'll put in zero point zero here and up here as well, or I'm actually doing the math and that should 82 00:05:22,520 --> 00:05:23,330 throw an error. 83 00:05:23,360 --> 00:05:23,780 Right. 84 00:05:24,030 --> 00:05:27,410 Let's see if it does restart the application. 85 00:05:27,410 --> 00:05:29,060 Go back here and reload the page. 86 00:05:29,060 --> 00:05:31,820 And here's why we can't do what I did just a minute ago. 87 00:05:32,390 --> 00:05:34,280 Cannot divide by zero immediately. 88 00:05:34,280 --> 00:05:36,230 Followed by one hundred. 89 00:05:36,230 --> 00:05:37,780 Divided by zero is zero. 90 00:05:37,790 --> 00:05:39,620 Well, that's not a true answer. 91 00:05:40,610 --> 00:05:42,260 Let's find out why I did that here. 92 00:05:42,260 --> 00:05:49,100 I have on line thirty in my application format F Pranav then the response writer then cannot divide 93 00:05:49,100 --> 00:05:50,810 by zero at that point. 94 00:05:50,810 --> 00:05:51,860 I want to return. 95 00:05:51,890 --> 00:05:53,960 I want to stop executing this function. 96 00:05:54,410 --> 00:05:55,310 So let's try it again. 97 00:05:59,660 --> 00:06:03,290 Reload cannot divide by zero, and that's what I'm looking for. 98 00:06:03,410 --> 00:06:08,150 All right, that's why we checked for errors already in the next election, we'll pick up with something 99 00:06:08,150 --> 00:06:09,530 a little more sophisticated.