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Programming Exercises - Terry Yin - Agile SG 2013

Presented in Agile Singapore 2013 Conference

Programming skills are so fundamental these days that people seem to take them for granted. However, a 10 year veteran might only have accumulated 1 year of experience as performing the same programming tasks over 10 years would not have resulted in 10 years' worth of skill development. To improve ones programming skills requires deliberate and intentional practice. This session will introduce a couple of ways to do programming exercises and will demonstrate the difference in their effectiveness. Terry will start you off on the journey to mastering the craft of programming.

Agile Singapore

November 07, 2013

Transcript

10. ProjectEuler.net • Project Euler is a series of challenging mathematical/computer

programming problems that requires more than just mathematical insights to solve. 10 "Project Euler exists to encourage, challenge, and develop the skills and enjoyment of anyone with an interest in the fascinating world of mathematics."

individually
14. Example: Quick & Dirty 14 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?

16. • 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. 16 int i, j, k, n, sum;! int factorial;! " int* getfactorial(int n)! {! factorial = 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;! }!

18. 18 Big number again. Ha ha, I did that before!

Let me reuse it...
19. #include<iostream>! " using namespace std;! " int i, j, k,

n, sum;! int factorial;! " int* getfactorial(int n)! {! factorial = 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;! } 19 Why the big number is named ‘factorial’ in my previous implementation? Where’s the code for big number?
20. 20 #include <stdio.h> " #define NUMB 120 // 9 *

120 = 1080 total digits. #define SIZE 1000000000 // 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; i < NUMB; i++) { bigNum1 = 0; bigNum2 = 0; bigNum3 = 0; } " bigNum1 = 1; bigNum2 = 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 >= 1) break; for (j = 0; j < NUMB; j++) { bigNum1[j] = bigNum2[j]; bigNum2[j] = bigNum3[j]; } } " printf("\n"); printf("P025 answer = %u", counter); } OK, too hard to reuse. It’s not that hard to invent the wheel again.
21. 21 Problem solving exercises ✓Train very important skills ✓Often used

as interview questions ✓Probably also train skills in making maintainable code, a little. •Don’t do it before bed time...

32. Code Retreat ✓-G[DQCTFQPN[ ✓7UGCRNCKPVGZVGFKVQT ✓4GCNN[UOCNNOGVJQFU ✓0QEQPFKVKQPU ✓0QNQQRU ✓0QRTKOKVKXGV[RGUQPKPVGTHCEG ✓0QTGVWTPXCNWGU 32

A day-long practice-intensive event for programmers, popularized by Corey Haines.

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

Try? 38
39. 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")); } " ...
40. Do deliberate exercises. Alone and with the others. Always use

good practices. Have fun. 40