WEBVTT 00:01.380 --> 00:05.160 Hello again! In this video, we're going to look into searching strings. 00:07.250 --> 00:13.460 The library string class has a member function called find. We can call this on a string, and it will look for 00:13.460 --> 00:16.160 the first occurrence of the argument in that string. 00:17.270 --> 00:23.020 So if we have some string object, then we call find, the argument to this could be a library string, 00:23.030 --> 00:23.480 of course. 00:23.900 --> 00:27.950 It can also be a single character, or it can be a C string. 00:30.170 --> 00:36.670 And then the function will perform a case-sensitive search, so if you try to find the letter capital 00:36.680 --> 00:39.860 'O', that won't succeed because we only have lower case 'o'. 00:39.860 --> 00:45.830 If the call succeeds, it returns the index of the first matching character. 00:46.460 --> 00:54.320 So for lower case 'o', that will be four. The index of that letter 'o'. For the argument "or" that will be 00:54.320 --> 00:59.510 seven, which is where the string appears, the C string. 01:01.280 --> 01:08.390 If the search does not succeed, it returns a special value, which is string double colon npos, and 01:08.390 --> 01:10.520 this represents an impossible index. 01:14.430 --> 01:20.670 So we've coded this up. So we have our string, "Hello world", and then we have the find operations. 01:21.690 --> 01:23.280 We check the return value. 01:23.910 --> 01:30.150 If the return value is not equal to string::npos, then we have a valid index and it has found something. 01:30.870 --> 01:32.190 And we print out the index. 01:32.550 --> 01:37.350 We're using raw strings, so we do not need to put back slashes inside the string. 01:38.880 --> 01:42.600 And if it is equal to npos, then we did not find it. 01:44.780 --> 01:50.730 So there's the single character, the C string, and then the search for capital 'O'. 01:53.900 --> 02:00.830 So there we are, the first occurrence of lowercase o is at index four. The string "or" is seven. 02:01.100 --> 02:04.040 And we could not find capital 'O' in that string. 02:09.420 --> 02:15.570 So we can actually use the returned value to index into the string and access the characters or modify 02:15.570 --> 02:15.810 them. 02:16.260 --> 02:20.490 But we need to make sure that we are actually using a valid index. 02:21.120 --> 02:24.810 So we should always check the index before actually using it. 02:28.260 --> 02:32.820 So here is that code, we're going to look for the first sequence of the letter 'o' again, and this time 02:32.820 --> 02:34.350 we're going to change it to 'p'. 02:36.570 --> 02:39.930 So we had "Hello world" and now we have "Hellp world"! 02:42.690 --> 02:48.420 We can also search for the last occurrence of a character. So there is rfind, which is a reverse 02:48.420 --> 02:48.900 find. 02:49.440 --> 02:54.730 So this will start at the end of the string and it will go back until it finds an occurrence. 02:54.750 --> 03:03.240 So if we do rfind of 'o', this will return the index of this letter 'o'. And if we do "or", that is 03:03.240 --> 03:04.680 going to be the same return value. 03:07.580 --> 03:12.830 So by default, this will start from the end of the string, the last character. We can change this 03:12.830 --> 03:14.260 by passing another argument. 03:14.280 --> 03:18.890 So if we have the argument five, that means it is going to start from the element with index 03:18.890 --> 03:22.520 five, which is this space character. 03:23.300 --> 03:26.150 So it's going to find the last occurrence of 'o' before the space. 03:28.630 --> 03:33.280 So here is the same program we had before, but now we are using rfind instead of find, and we are 03:33.280 --> 03:37.060 going to change the last matching character. 03:37.180 --> 03:38.290 So now it is 03:38.620 --> 03:39.070 "Hello wprld"! 03:42.830 --> 03:46.730 So that's searching for a single character or a single string. 03:47.330 --> 03:51.560 We can also search for one of a group of characters. 03:53.070 --> 03:56.230 To do that, we use the member function find_first_of. 03:56.880 --> 03:58.170 So we give this a string. 03:58.650 --> 04:02.020 The string contains the letters that we are looking for. 04:02.040 --> 04:07.080 So we are looking for one of "aeiou" in the "Hello world" string. 04:08.340 --> 04:12.390 So this is going to be turned the first of these, which is going to be the 'e' from "hello". 04:13.530 --> 04:19.470 There is also a find_last_of, which will return the index of the last occurrence of any of these characters. 04:20.160 --> 04:21.900 So that's going to be the 'o' in "world". 04:23.600 --> 04:28.580 And you can also invert this. So you can find the first character that is not a vowel. 04:29.330 --> 04:31.310 So that is going to be the 'H' of "hello". 04:32.210 --> 04:35.090 And you can find the last character that is not one of these. 04:35.810 --> 04:37.930 So that's going to be the 'd' in "world". 04:40.580 --> 04:48.010 So here we are, we are just going to find the first and last voewl and non-vowel. So the first vowel 04:48.010 --> 04:50.840 is at index one. The last one is at index seven. 04:51.560 --> 04:56.800 The first non-vowel is index zero, which is 'H', and the last non-vowel is index 04:56.810 --> 04:58.100 10, which is 'd'. 04:58.880 --> 05:01.550 So if you want a little exercise, you can change this program. 05:01.550 --> 05:03.950 So it actually prints out these characters. 05:05.270 --> 05:07.280 Okay, so that's it for this video. 05:07.640 --> 05:08.480 I'll see you next time. 05:08.480 --> 05:10.730 But meanwhile, keep coding!