WEBVTT 00:00.860 --> 00:09.650 So to return back to input because now we have the tools necessary to start talking about input errors. 00:09.950 --> 00:13.160 So let's say we hand this example here. 00:13.180 --> 00:31.000 I say number one is to know three and in roots and say please input three integers. 00:34.330 --> 00:37.570 Yes these. 00:37.580 --> 00:38.040 Between 00:50.320 --> 00:51.630 rows can we get them 00:54.390 --> 00:57.980 and we're going to really output. 00:58.070 --> 01:00.050 It's a very simple program. 01:30.330 --> 01:31.170 OK. 01:31.930 --> 01:38.200 So let's run this in ch should see. 01:38.200 --> 01:41.620 So let's say we get 30 20 and 10. 01:41.620 --> 01:48.450 So the integers you input were 30 20 and 10 so far so good. 01:48.680 --> 01:52.960 So let's say we had 30 Fred and 10. 01:53.390 --> 01:57.750 So Fred is clearly not an integer right. 01:57.860 --> 02:01.740 So let's see what happens if we do this. 02:01.770 --> 02:07.960 So the integers you input were 30 zero and zero. 02:08.020 --> 02:11.150 So why did this happen. 02:11.260 --> 02:19.390 Well it's because we didn't get the proper input for number two because there was a type mismatch. 02:19.390 --> 02:22.860 So Fred is non-integer right. 02:23.350 --> 02:28.040 And because we we got a type mismatch. 02:28.180 --> 02:38.740 This actually puts our CNN into a failed state and once it's in a failed state it doesn't read input 02:38.740 --> 02:39.330 anymore. 02:39.340 --> 02:49.090 So that's why we don't get you know the 10 at least for the number three right because we input the 02:49.090 --> 02:52.300 first and last numbers correctly. 02:52.300 --> 02:55.170 But we didn't input the second one correctly. 02:55.360 --> 03:05.770 So as soon as there is some kind of failure with C in it it propagates to everything. 03:06.190 --> 03:09.450 So now we can't read any input at all. 03:09.820 --> 03:14.910 So how do we detect when we're in this failed state. 03:15.160 --> 03:22.790 Well to do that we actually have to use something called seen datt fail. 03:23.860 --> 03:27.040 So rewrite this a little bit and say If 03:30.050 --> 03:39.650 CN fail this this really says If CN is in a failure state. 03:39.650 --> 03:40.670 Right. 03:40.850 --> 03:49.020 Remember that if you have some kind of type mismatch then that'll put C in into a failure state. 03:49.350 --> 03:52.570 Then then we have to do something. 03:52.570 --> 03:57.280 So how do we fix this failure state. 03:57.280 --> 04:11.690 So to do that we have to say see in clear and see and clear does is it really just takes away the failure 04:11.690 --> 04:17.340 state it puts it back into hey you can read again that's all it's really saying. 04:17.360 --> 04:23.040 You can you can read again from CNN or the cons.. 04:23.540 --> 04:24.470 OK. 04:24.470 --> 04:31.450 So let's do that and let's try to read everything again. 04:31.590 --> 04:32.780 Nice coffee this 04:37.970 --> 04:45.220 settlers just going to do this check after each time we read something from the input 04:53.480 --> 04:55.660 in see what happens. 04:58.020 --> 05:01.590 30 Fred and 10. 05:02.310 --> 05:04.710 So nothing changed. 05:04.750 --> 05:05.750 Sure. 05:06.390 --> 05:19.200 And this is because like I said all clear does is clear is essentially a flag in C in that says hey 05:19.380 --> 05:28.200 you can read again but it didn't actually take out the offending input. 05:28.200 --> 05:29.820 In this case Fred. 05:30.180 --> 05:41.060 So we actually have to take out the input that is messing us up and how we can do that is to say see 05:41.060 --> 05:42.710 in a more 05:46.140 --> 05:49.610 answers and say See. 05:49.690 --> 05:51.640 Ignore. 05:51.680 --> 06:01.280 So what this does is it ignores from where it's reading from or where it's currently at it's going to 06:01.280 --> 06:14.880 ignore 256 characters or up to a space so it would either ignore 256 characters or up to a space so 06:14.880 --> 06:19.520 we're putting everything between with spaces. 06:24.300 --> 06:27.330 So we're putting everything with spaces in between. 06:27.330 --> 06:31.100 So this should work pretty nicely. 06:31.170 --> 06:34.020 So let's just copy this 06:37.460 --> 06:44.000 image going to put that after each clear and it has to be after that clear because otherwise it won't 06:44.570 --> 06:48.200 it won't accept any operations we see in the wires. 06:51.200 --> 06:59.040 So let's run this mercy 30 Fred and 10. 06:59.240 --> 07:08.710 And now it is at least had at least read the last number. 07:09.250 --> 07:12.270 So it failed on Fred again. 07:12.490 --> 07:20.040 But at least it recovered by saying right here is the name the next number. 07:20.070 --> 07:26.260 Number two said yes I'm in a failure state it cleared the failure state and then ignored up until the 07:26.260 --> 07:27.440 space ignored. 07:27.460 --> 07:34.560 Every character up until this space right before the 10. 07:34.810 --> 07:42.650 And then that fixed it so seeing could read at least the last number. 07:42.660 --> 07:50.430 So this is still not really ideal because it still skips number two. 07:50.670 --> 08:00.740 So be what we think you really want is to riprap the user every time they make a mistake. 08:00.830 --> 08:08.690 So any time they make some kind of silly mistake we want to riprap the user and say hey can you please 08:08.690 --> 08:11.630 try again please try again. 08:11.960 --> 08:20.760 So let's kind of rewrite this whole thing and let's try to use a loop in order to do this. 08:22.070 --> 08:29.100 So let's say it numb in the pool feel your 08:32.120 --> 08:38.100 numbers are b your input and explain the failure in the second. 08:38.180 --> 08:41.390 So you can use a do while loop. 08:41.480 --> 08:45.650 So this is going to be quite useful for us. 08:45.820 --> 08:47.170 While failure 08:50.160 --> 08:56.410 so failure is if there was an input failure we want to try again. 08:57.270 --> 09:07.110 So if we have a failure in the input We'll set the failure to be true and that will really or will redo 09:07.110 --> 09:09.000 this whole loop. 09:09.380 --> 09:14.940 It's a failure going to set to false at the beginning because there is no failure yet. 09:16.780 --> 09:18.210 And we're going to prompt. 09:18.440 --> 09:29.700 So please enter a number it's in Numb 09:34.400 --> 09:42.570 Arend do the same thing we did for if there was a failure in C in say C and that clear clear the failure 09:43.930 --> 09:45.580 and ignore 09:50.630 --> 09:51.780 it. 09:52.120 --> 10:02.550 You want a constant here actually costs to inch nor characters to six of them. 10:07.110 --> 10:10.080 Nor dares. 10:10.120 --> 10:16.960 And instead of a space we're going to use the Enter key because there's only going to be one input to 10:16.960 --> 10:18.550 be read here. 10:19.530 --> 10:25.930 So we don't we don't need spaces here and we're going to set the failure to be true because there was 10:25.930 --> 10:27.300 a failure. 10:27.300 --> 10:27.900 Okay. 10:28.210 --> 10:34.170 And then we're output to the user that there was an input error 10:36.660 --> 10:47.720 error and we're going to say please try again. 10:48.380 --> 10:57.960 So notice that we're using a do while loop and that's because we want to prompt the user at least once. 10:58.380 --> 10:58.800 Right. 10:58.940 --> 11:05.350 So we want to do this this whole thing one time at least OK. 11:05.410 --> 11:08.400 So this is why do Weill's are actually useful. 11:08.440 --> 11:16.150 They're very useful in this case and in this course for input from the user because the user could mess 11:16.150 --> 11:17.430 up. 11:17.530 --> 11:24.690 So we want to get the input checked to see if there is a failure with that inputs. 11:24.910 --> 11:30.720 So say he so say we wanted a number but he typed Fred that would have it. 11:30.760 --> 11:34.950 That would be a type mismatch because characters are not numbers. 11:35.050 --> 11:44.780 And then we would clear that failure and ignore the characters up until they hit the enter key. 11:45.040 --> 11:50.830 So that's I you know you always have to press the enter key and we just set the failure to be true. 11:51.160 --> 11:55.050 And we just say hey please try again. 11:55.500 --> 11:56.640 Then output 11:59.810 --> 12:09.660 number you in the head most no. 12:10.250 --> 12:17.540 So we know at this point online 35 that there was no failure at this point. 12:18.540 --> 12:23.840 Thus we just put the number they that they that they input inputted. 12:23.970 --> 12:26.660 So let's run this and see what happens. 12:27.120 --> 12:28.230 So say Fred 12:32.190 --> 12:35.700 and see we have actually a formatting problem. 12:37.010 --> 12:39.170 So we've got to have the Endal here. 12:39.350 --> 12:42.720 So let's put that there stop 12:46.050 --> 12:48.580 and put it number Fred. 12:48.730 --> 12:51.370 So please try again. 12:51.400 --> 12:53.130 Let's try it again. 12:53.230 --> 13:01.020 See Fred again not letting us write any kind of character put. 13:01.120 --> 13:03.530 It's not allowing us to do that. 13:03.910 --> 13:04.900 OK. 13:04.930 --> 13:09.340 So it's just 10 a the input was 10 right. 13:10.300 --> 13:19.650 So this is one nice thing about do while loops is that for input you always kind of want to do it at 13:19.650 --> 13:21.110 least one time. 13:21.380 --> 13:21.920 Right. 13:22.110 --> 13:27.570 Because you always want to give the user a chance to input something if they mess up though that we 13:27.570 --> 13:29.860 can actually do it again. 13:31.050 --> 13:31.880 OK. 13:32.150 --> 13:37.890 So in the next next lecture we'll do some practice problems using GPS.