1
00:00:07,860 --> 00:00:12,235
The last thing I want to talk about in this lesson is hard coding,

2
00:00:12,235 --> 00:00:17,140
and before I get to that I'm just going to tell a motivating story from my childhood.

3
00:00:17,140 --> 00:00:22,560
So, I have three older siblings and when they were doing algebra,

4
00:00:22,560 --> 00:00:24,645
if you remember algebra,

5
00:00:24,645 --> 00:00:27,480
then you often get problems of the type: solve for x,

6
00:00:27,480 --> 00:00:29,550
solve for y, solve for z.

7
00:00:29,550 --> 00:00:32,110
One day, I overheard my sister talking on

8
00:00:32,110 --> 00:00:35,195
the phone with a friend about a math problem that they had,

9
00:00:35,195 --> 00:00:40,635
and they were trying to solve for the value of x and I overheard my sister saying,

10
00:00:40,635 --> 00:00:42,420
"The value of x is three."

11
00:00:42,420 --> 00:00:43,990
When I heard that,

12
00:00:43,990 --> 00:00:48,760
I thought that I had found out some hidden secret about algebra. X is three.

13
00:00:48,760 --> 00:00:52,160
I could take every single problem that involves x and just

14
00:00:52,160 --> 00:00:56,510
substitute three and I'd crack the code and I didn't have to learn algebra anymore.

15
00:00:56,510 --> 00:00:58,195
I could just skip that grade.

16
00:00:58,195 --> 00:01:00,615
Of course, if you've actually taken algebra,

17
00:01:00,615 --> 00:01:02,715
then you know that x isn't three.

18
00:01:02,715 --> 00:01:06,315
You know that you have to solve for the value of x every single time.

19
00:01:06,315 --> 00:01:10,585
So, what I was thinking of doing there was a form of hard-coding,

20
00:01:10,585 --> 00:01:14,650
or thinking that x is three for every single problem.

21
00:01:14,650 --> 00:01:19,505
So, in the context of solving Python programs, what hard-coding is,

22
00:01:19,505 --> 00:01:21,740
is it's writing down the answer without

23
00:01:21,740 --> 00:01:24,830
actually going through the work of computing the answer.

24
00:01:24,830 --> 00:01:27,440
So, let's suppose that I want to write

25
00:01:27,440 --> 00:01:31,085
a program to print out the value of x and y averaged.

26
00:01:31,085 --> 00:01:36,670
So, if I have x equal to 10 and y equal to 20,

27
00:01:36,670 --> 00:01:42,705
then I could hard-code my answer by saying average equals 15.0,

28
00:01:42,705 --> 00:01:44,400
and I, let's say,

29
00:01:44,400 --> 00:01:48,825
print out that average,

30
00:01:48,825 --> 00:01:52,940
and so yes, in this case I happened to get the right answer,

31
00:01:52,940 --> 00:01:56,060
that the average of x and y is 15,

32
00:01:56,060 --> 00:02:00,115
but my answer is hard-coded because I said that the average was 15,

33
00:02:00,115 --> 00:02:04,850
and what that means is that if I change the value of x here to be 30,

34
00:02:04,850 --> 00:02:07,550
the average should be 25.0,

35
00:02:07,550 --> 00:02:11,650
but instead I still get 15 because my answer was hard-coded.

36
00:02:11,650 --> 00:02:13,605
So, what I'll do is,

37
00:02:13,605 --> 00:02:17,035
instead of writing out average equals 15,

38
00:02:17,035 --> 00:02:19,460
I want to actually write out the expression that's going

39
00:02:19,460 --> 00:02:22,425
to reference x and y to compute that average.

40
00:02:22,425 --> 00:02:29,815
So, I'll say average equals x plus y divided by two, and so,

41
00:02:29,815 --> 00:02:33,020
even though I still get the same answer of 15,

42
00:02:33,020 --> 00:02:36,050
then because this answer is no longer hard-coded,

43
00:02:36,050 --> 00:02:38,770
if I change the value of x to 30,

44
00:02:38,770 --> 00:02:41,010
then my answer is still going to be correct.

45
00:02:41,010 --> 00:02:45,640
Same thing if I change the value of my answer, y, to 40.

46
00:02:45,640 --> 00:02:47,880
So, in your assignments,

47
00:02:47,880 --> 00:02:50,760
we'll often say, "Don't hard-code your answer."

48
00:02:50,760 --> 00:02:54,830
What that means is that you have to write expressions that actually reference

49
00:02:54,830 --> 00:02:59,000
the variables and rather than just jumping straight to the answer,

50
00:02:59,000 --> 00:03:02,210
you actually have to write expressions and statements that will actually

51
00:03:02,210 --> 00:03:06,670
compute the answer in your code. Until next time.