WEBVTT 00:00:00.700 --> 00:00:05.991 Our task is to classify three scores and total only the passing results. 00:00:06.141 --> 00:00:13.431 This is a useful size for learning control flow: the input is small enough to check by hand, and the 00:00:13.431 --> 00:00:14.525 decisions are visible. 00:00:14.675 --> 00:00:21.890 We will define one function, loop over a list, skip unwanted values, and finish with a bounded while 00:00:21.890 --> 00:00:22.291 loop. 00:00:22.441 --> 00:00:29.395 The full downloadable program includes definitions before calls, so you can run it as a single file. 00:00:31.550 --> 00:00:34.963 A function gives a reusable operation a name. 00:00:35.113 --> 00:00:42.345 Score is its parameter, so each call can classify a different number without repeating the decision tree. 00:00:42.495 --> 00:00:47.125 Return sends the result back to the caller and ends that function call. 00:00:47.275 --> 00:00:52.757 This function returns a string in every branch, which keeps its behavior predictable. 00:00:52.907 --> 00:00:59.073 Read the thresholds aloud: at least ninety, otherwise at least sixty, otherwise retry. 00:00:59.223 --> 00:01:02.529 The order makes the categories mutually exclusive. 00:01:04.680 --> 00:01:08.797 Boundary values are more revealing than a few random inputs. 00:01:08.947 --> 00:01:15.495 Ninety should enter the first branch; sixty should enter the second; fifty nine should reach the last 00:01:15.495 --> 00:01:15.881 branch. 00:01:16.031 --> 00:01:21.833 If we tested only ninety eight, a mistaken passing threshold could go unnoticed. 00:01:21.983 --> 00:01:26.719 These are small executable checks, not a complete grading system. 00:01:26.869 --> 00:01:34.750 For a real application you would also decide what to do with missing values, non numeric input, and 00:01:34.750 --> 00:01:36.939 scores outside the allowed range. 00:01:39.090 --> 00:01:42.226 The for loop introduces score for each list entry. 00:01:42.376 --> 00:01:49.284 Total lives outside the loop because we need to carry it from one iteration to the next and read it 00:01:49.284 --> 00:01:49.629 afterward. 00:01:49.779 --> 00:01:55.731 Continue skips the rest of the current iteration, so fifty five never reaches the addition. 00:01:55.881 --> 00:01:58.868 The final total is one hundred seventy. 00:01:59.018 --> 00:02:04.138 Notice that classify returns a label, while this loop accumulates a number. 00:02:04.288 --> 00:02:09.536 Keeping those responsibilities separate makes both pieces easier to understand. 00:02:11.690 --> 00:02:13.610 Break ends the loop completely. 00:02:13.760 --> 00:02:16.661 Continue only skips the current iteration. 00:02:16.811 --> 00:02:22.379 With this particular input, break prints the first two scores and stops at the failing one. 00:02:22.529 --> 00:02:28.868 Add another passing score after fifty five to see the difference clearly: continue would still consider 00:02:28.868 --> 00:02:30.849 it, while break would not. 00:02:30.999 --> 00:02:33.901 Choose the control statement from the task meaning. 00:02:34.051 --> 00:02:40.429 A report that needs every passing score should not stop just because one earlier entry failed. 00:02:42.580 --> 00:02:45.716 While checks a condition before each iteration. 00:02:45.866 --> 00:02:52.941 Here the counter starts at zero and moves toward the stopping condition on every pass, so the output is 00:02:52.941 --> 00:02:54.058 one, two, three. 00:02:54.208 --> 00:02:58.624 A loop without that update would keep satisfying the same condition. 00:02:58.774 --> 00:03:04.107 Before writing a while loop, identify what changes and why the loop will end. 00:03:04.257 --> 00:03:10.679 For visiting an existing collection, a for loop often makes that termination behavior simpler to see. 00:03:12.830 --> 00:03:18.313 A closure expresses a small function that we can pass into another operation. 00:03:18.463 --> 00:03:22.004 Here apply calls its callback with the supplied value. 00:03:22.154 --> 00:03:28.085 The closure parameter appears before the arrow, and the expression after it computes the result. 00:03:28.235 --> 00:03:35.637 This example also previews the pipe syntax we will study next: twenty one becomes the input to apply. 00:03:35.787 --> 00:03:39.051 Soon we will pass closures into stream operators. 00:03:39.201 --> 00:03:42.465 Keep each closure focused on a small transformation. 00:03:44.620 --> 00:03:47.585 This version runs, but the logic is wrong. 00:03:47.735 --> 00:03:54.477 A score of ninety eight already satisfies the first branch, so the excellent branch cannot receive it. 00:03:54.627 --> 00:03:58.616 A syntax check cannot infer your intended grading rules. 00:03:58.766 --> 00:04:03.971 Put the more specific high threshold first, then rerun the boundary examples. 00:04:04.121 --> 00:04:11.718 This is why running a program once without an error is not enough: correct syntax and correct answers are 00:04:11.718 --> 00:04:14.916 separate things that require different kinds of checking. 00:04:17.070 --> 00:04:24.366 Extend the input with one hundred and sixty, predict the new total, and add a counter for passing scores. 00:04:24.516 --> 00:04:30.489 Keep the counter update beside the addition so both use the same filtering decision. 00:04:30.639 --> 00:04:33.050 Then test the threshold values again. 00:04:33.200 --> 00:04:40.447 You have now combined function calls, returned values, branching, iteration, and mutable state in one 00:04:40.447 --> 00:04:41.413 small task. 00:04:41.563 --> 00:04:47.153 In the next lesson we will express a sequence of transformations with the pipe operator.