Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:00,580 --> 00:00:01,960 Now up to this point, 2 00:00:01,990 --> 00:00:06,640 we've only been using for loops in association with lists. 3 00:00:07,030 --> 00:00:11,830 So we've been looping through the list and getting hold of each of the items in 4 00:00:11,830 --> 00:00:14,200 the list and then doing something with it, right? 5 00:00:14,740 --> 00:00:18,940 But we're not always going to be working with lists and using for loops. 6 00:00:19,390 --> 00:00:23,920 Sometimes we might want to use a loop completely independent of a list. 7 00:00:24,640 --> 00:00:29,080 And a good example of this is when Carl Gauss the German 8 00:00:29,080 --> 00:00:32,380 mathematician was just a child when he was 10 years old, 9 00:00:32,710 --> 00:00:36,790 his math teacher gave him an exercise that she probably thought would tie him up 10 00:00:36,790 --> 00:00:37,623 for it a little while. 11 00:00:38,080 --> 00:00:43,080 And the idea was to get him to add all of the numbers from 1 to 100. 12 00:00:43,990 --> 00:00:47,470 So 1 + 2 + 3 + 4 + 5, et cetera, 13 00:00:47,710 --> 00:00:49,660 all the way until a hundred. 14 00:00:50,500 --> 00:00:54,010 And even though she thought this would keep him busy for an hour or so getting 15 00:00:54,010 --> 00:00:58,000 this young child to add up these numbers and I can have some peace and quiet 16 00:00:58,000 --> 00:00:59,020 scrolling on Facebook, 17 00:00:59,440 --> 00:01:03,160 but unfortunately he came back to her within two minutes and gave her the 18 00:01:03,160 --> 00:01:06,880 answer. So how did he work it out? Well, 19 00:01:06,910 --> 00:01:11,140 here's actually a really smart kid and he figured out that if you flip the 20 00:01:11,140 --> 00:01:14,560 numbers around, so 100 + 99 + 98, 21 00:01:14,950 --> 00:01:17,650 and you'll look at both of these two lines, 22 00:01:17,980 --> 00:01:21,700 you can see that 1 + 100 = 101, 2 23 00:01:21,700 --> 00:01:26,410 + 99 = 101, 3 + 98 = 101, basically, 24 00:01:26,410 --> 00:01:28,450 if you tie all of these numbers together, 25 00:01:28,720 --> 00:01:31,690 there's actually 50 pairs of 101. 26 00:01:31,960 --> 00:01:36,960 So he could simply just do 50 multiplied by 101 which is 5,050. 27 00:01:38,080 --> 00:01:39,790 And that's how he figured out the answer. 28 00:01:40,450 --> 00:01:45,450 But we can actually outshine Gaus because we can do this calculation in less 29 00:01:45,670 --> 00:01:50,230 than a minute, just by writing a few lines of code. But in order to do this, 30 00:01:50,380 --> 00:01:55,380 we first have to learn about using for loops with the range function. 31 00:01:56,770 --> 00:02:00,460 Now the range function is something that is really, really helpful 32 00:02:00,760 --> 00:02:04,510 if you want to generate a range of numbers to loop through. 33 00:02:05,290 --> 00:02:08,230 And the syntax looks something like this. 34 00:02:08,410 --> 00:02:12,940 So we've still got our for and our in keywords highlighted in blue, 35 00:02:13,570 --> 00:02:16,540 but instead of looping through a list, 36 00:02:17,050 --> 00:02:21,910 we define how our loop is going to work by creating a range. 37 00:02:22,300 --> 00:02:23,050 So in this case, 38 00:02:23,050 --> 00:02:28,050 I'm creating a range between a and b and then I'm going to get hold of each 39 00:02:29,050 --> 00:02:32,320 number in that range and do something with that number. 40 00:02:33,700 --> 00:02:38,200 So for example, if I wrote for number in range, 41 00:02:38,560 --> 00:02:42,130 and then my range is going to be 1, 10. 42 00:02:42,520 --> 00:02:46,510 So this is going to be the range that I'm going to create between 1 and 10 43 00:02:46,870 --> 00:02:50,470 and then I want to get hold of each of the numbers inside that range. 44 00:02:50,980 --> 00:02:55,810 And this is going to be between 1 and 10 and not including 10. 45 00:02:56,170 --> 00:03:00,340 So if I go ahead and print out the number that I create from my for loop, 46 00:03:00,820 --> 00:03:05,800 then you'll see that what happens is it prints 1 2 3 4 5 47 00:03:05,800 --> 00:03:10,210 6 7 8 9, but not the last digit, which I've included here. 48 00:03:10,660 --> 00:03:14,680 So if I wanted all of the numbers from 1 to 10, 49 00:03:15,010 --> 00:03:17,920 I actually have to set a range between 1 and 11. 50 00:03:18,610 --> 00:03:20,230 And now when you run the code, 51 00:03:20,290 --> 00:03:23,050 you can see that it goes from 1 all the way up to 10. 52 00:03:24,580 --> 00:03:26,320 Now by default, 53 00:03:26,380 --> 00:03:31,380 the range function will step through all the numbers from the start to the end, 54 00:03:32,710 --> 00:03:35,170 and it will increase by 1. Now, 55 00:03:35,170 --> 00:03:37,870 if you want it to increase by any other number, 56 00:03:38,020 --> 00:03:43,020 then you have to add another comma to the end of it and specify how large you 57 00:03:44,140 --> 00:03:48,910 want the step to be. So let's say we changed the step size to three. 58 00:03:49,390 --> 00:03:51,610 Now, if I rerun the same code, 59 00:03:51,850 --> 00:03:55,930 you'll see that it goes from one and then it steps by three to four and then it 60 00:03:55,930 --> 00:03:59,260 steps by three. And then it steps by three, finally to 10. 61 00:04:01,000 --> 00:04:04,180 Now let's come back to the problem that I mentioned at the beginning of this 62 00:04:04,180 --> 00:04:05,013 lesson. 63 00:04:05,170 --> 00:04:10,170 How can we add up all of the numbers from 1 to 100 by using code? 64 00:04:10,720 --> 00:04:11,020 Well, 65 00:04:11,020 --> 00:04:14,590 it's going to involve a for loop and it's going to involve the range function 66 00:04:15,070 --> 00:04:20,070 because we're going to get hold of every number in the range between 1 and 67 00:04:20,770 --> 00:04:21,490 100, 68 00:04:21,490 --> 00:04:26,050 so we need to write 101. Once we've got hold of all of these numbers, 69 00:04:26,110 --> 00:04:29,830 it's as simple as using a accumulator, 70 00:04:29,860 --> 00:04:34,810 so let's say a total = 0. And then inside the for loop, 71 00:04:34,810 --> 00:04:36,100 so that means indented, 72 00:04:36,370 --> 00:04:41,370 we're going to say total += number. 73 00:04:43,090 --> 00:04:48,090 So now it's going to add every number in this range to the total starting from 74 00:04:48,790 --> 00:04:49,623 zero. 75 00:04:49,900 --> 00:04:54,760 And this is basically going to give us the sum of every number from 1 to 100. 76 00:04:55,150 --> 00:04:59,770 So let's go ahead and print it out and see if it matches Gauss's value. 77 00:05:01,690 --> 00:05:04,570 And there you have it 5,050. 78 00:05:05,440 --> 00:05:09,160 So now that we've beaten Gauss at his own game of math using programming, 79 00:05:09,430 --> 00:05:13,240 let's head over to the next lesson and try to complete a challenge using the 80 00:05:13,240 --> 00:05:17,770 range function to see if you managed to internalize and understand everything we 81 00:05:17,770 --> 00:05:21,760 talked about in this lesson. So for all of that and more, I'll see you there. 7780