This is a motivational talk about practicing programming skills as a professional programmer. I gave the talk many times in many conferences and companies. You can find the video of me giving the talk on this here (in Chinese): http://v.youku.com/v_show/id_XMzI3OTI1MDQw.html I did the talk in English as well, but there's no video online.

1. Programming
Exercises
Terry Yin

2. Who am I?
2

3. Why Programming Exercises?
3

4. 4

5. Quality vs. Quantity
5

6. Gamification
6

7. Question
Does software company need to
train programmers?
7

8. Leonhard Euler
Dojo
vs.
8

9. What is ProjectEuler.net?
9

10. ProjectEuler.net
"Project Euler exists to encourage, challenge, and develop the skills and enjoyment of anyone with
an interest in the fascinating world of mathematics."
• Project Euler is a series of challenging mathematical/computer
programming problems that requires more than just mathematical
insights to solve.
10

11. ProjectEuler.net
11

12. ProjectEuler.net
12

13. Expectations
Mathematics
lution implementing
So
rfor mance co d ing
Hig h pe
So lving problem
ind ivi dually
13

14. Example: Quick & Dirty
Once you solved a problem, you are entitled to join the forum for this problem.You can
share your solution with the other people who have also solved it. And the post usually
start with this sentence:!
Good coding habit?
14

15. Another Example
15

16. int i, j, k, n, sum;!
int factorial[10000];!
"
• It’s too simple for
•
•
Java, Ruby or Python,
for which they can
handle big numbers by
default."
So let’s look at C/C++."
Real code copied from
the forum.
int* getfactorial(int n)!
{!
factorial[0] = 1;!
k = 0;!
for(i = 2; i <= n; i++)!
{!
for(j = 0; j <= k; j++)!
factorial[j] *= i;!
for(j = 0; j <= k; j++)!
{!
if(factorial[j] >= 10)!
{!
factorial[j+1] += (factorial[j] - (factorial[j] % 10)) / 10;!
factorial[j] = factorial[j] % 10;!
if(j == k)!
k++;!
}!
}!
}!
return factorial;!
}!
"
int getsum(int* array, int k)!
{!
sum = 0;!
for(i = 0; i <= k; i++)!
sum += array[i];!
return sum;!
}!
"
int main()!
{!
int* factorial = getfactorial(n);!
sum = getsum(factorial, k);!
cout << "nThe sum of the digits of " << n << "! is " << sum << ".n";!
return 0;!
16
}!

17. 17

18. Big number again. Ha ha, I did that
before! Let me reuse it...
18

19. #include<iostream>!
"
using namespace std;!
"
int i, j, k, n, sum;!
int factorial[10000];!
"
Why the big number is named ‘factorial’
in my previous implementation?
int* getfactorial(int n)!
{!
factorial[0] = 1;!
k = 0;!
for(i = 2; i <= n; i++)!
{!
for(j = 0; j <= k; j++)!
factorial[j] *= i;!
for(j = 0; j <= k; j++)!
{!
if(factorial[j] >= 10)!
{!
factorial[j+1] += (factorial[j] - (factorial[j] % 10)) / 10;!
factorial[j] = factorial[j] % 10;!
if(j == k)!
k++;!
}!
}!
}!
return factorial;!
}
Where’s the code for big number?
19

20. #include <stdio.h>
"
#define NUMB 120
#define SIZE 1000000000
"
OK, too hard to reuse. It’s not
that hard to invent the wheel again.
// 9 * 120 = 1080 total digits.
// 9 digit numbers
int main() {
int i = 0;
int j = 0;
int bigNum1[NUMB];
int bigNum2[NUMB];
int bigNum3[NUMB];
int counter = 0;
"
"
"
"
}
for (i = 0;
bigNum1 =
bigNum2 =
bigNum3 =
}
i < NUMB; i++) {
0;
0;
0;
bigNum1[0] = 1;
bigNum2[0] = 1;
counter = 2;
i = 0;
while (i == 0) {
counter++;
for (j = 0; j < NUMB; j++) {
bigNum3[j] = bigNum2[j] + bigNum1[j];
}
for (j = 0; j < NUMB-1; j++) {
while (bigNum3[j] >= SIZE) {
bigNum3[j] -= SIZE;
bigNum3[j+1]++;
}
}
if (bigNum3[111] >= 1)
break;
for (j = 0; j < NUMB; j++) {
bigNum1[j] = bigNum2[j];
bigNum2[j] = bigNum3[j];
}
}
printf("n");
printf("P025 answer = %u", counter);
20

21. s
ng exercise
i
oblem so lv
Pr
tant skills
ver y impor
✓ Train
inter view
s
ten use d a
Of
✓
ques tions
n skills in
i
ly also tra
✓ Probab
able co de,
n
ng maintai
maki
a little.
•Don’t do it before bed time...
21

22. What is Cyber Dojo?
22

23. 23

24. 24

25. 25

26. RED - GREEN - REFACTOR
26

27. Functional Test
Integration Test
Unit Test
27

28. 28

29. 29

30. 30

31. Refactoring Dojo
31

32. Code Retreat
A day-long practice-intensive event for programmers, !
popularized by Corey Haines.
✓
✓
✓
✓
✓
✓
✓
32

33. Which One Do You Prefer?
33

34. Poker Hands
34

35. Poker Hands Kata
35

36. Poker Hands in ProjectEuler
• This is not a very hard problem to solve,
•
comparing to most of the problems listed in
ProjectEuler.net"
But it’s hard to solve it without bugs if you don’t
have unit tests."
• Problem 54 in projectEuler.net
36

37. Example: Complicated
Transaction
37

38. Why Did I Do It Right
With Only One Try?
38

39. TEST(poker_hand, comparing){
CHECK(pokerHand("4H 5C 6S 7S TD")< pokerHand("2C 3S 7S 8D KD"));
CHECK(!(pokerHand("4H 5C 6S 7S KD")< pokerHand("2C 3S 7S 8D TD")));
CHECK(pokerHand("4H 5C 6S 7S KD")> pokerHand("2C 3S 7S 8D TD"));
}
TEST(poker_hand, compare_cards){
CHECK(pokerHand("3H 5C 6S 7S 8D")< pokerHand("4H 5C 6S 7S 9D"));
CHECK(pokerHand("3H 5C 6S 7S 9D")< pokerHand("4H 5C 6S 7S TD"));
CHECK(pokerHand("3H 5C 6S 7S TD")< pokerHand("4H 5C 6S 7S JD"));
CHECK(pokerHand("3H 5C 6S 7S JD")< pokerHand("4H 5C 6S 7S QD"));
CHECK(pokerHand("3H 5C 6S 7S QD")< pokerHand("4H 5C 6S 7S KD"));
CHECK(pokerHand("3H 5C 6S 7S KD")< pokerHand("4H 5C 6S 7S AD"));
}
TEST(poker_hand, compare_high_cards_2nd){
CHECK(pokerHand("3H 5C 6S 7S 9D")< pokerHand("3H 5C 6S 8S 9D"));
}
TEST(poker_hand, compare_high_cards_3nd_4th_5th){
CHECK(pokerHand("3H 5C 6S 8S 9D")< pokerHand("3H 5C 7S 8S 9D"));
CHECK(pokerHand("3H 4C 7S 8S 9D")< pokerHand("3H 5C 7S 8S 9D"));
CHECK(pokerHand("2H 5C 7S 8S 9D")< pokerHand("3H 5C 7S 8S 9D"));
}
TEST(poker_hand, compare_high_card_and_one_pair){
CHECK(pokerHand("3H 5C 6S 8S 9D")< pokerHand("3H 5C 7S 8S 8D"));
}
TEST(poker_hand, compare_one_pairs){
CHECK(pokerHand("3H 5C 6S 9S 9D")> pokerHand("3H 5C 7S 8S 8D"));
CHECK(pokerHand("5C 6S 9S 9D KD")> pokerHand("5C 7S 8S 8D AD"));
CHECK(pokerHand("5C 6S 9S 9D KD")< pokerHand("5C 7S 9S 9D AD"));
}
"
...
39

40. Do deliberate exercises.
Alone and with the others.
Always use good practices.
Have fun.
40