劣质代码评析——《写给大家看的C语言书(第2版)》附录B之21点程序(六)
0. #include <stdio.h> 1. #include <time.h> 2. #include <ctype.h> 3. #include <stdlib.h> 4. 5. #define BELL '\a' 6. #define DEALER 0 7. #define PLAYER 1 8. 9. #define ACELOW 0 10. #define ACEHIGH 1 11. 12. int askedForName = 0; 13. 14. 15. void dispTitle(void); 16. void initCardsScreen(int cards[52],int playerPoints[2], 17. int dealerPoints[2], int total[2], 18. int *numCards); 19. int dealCard(int * numCards,int cards[52]); 20. void dispCard(int cardDrawn,int points[2]); 21. void totalIt(int points[2],int tatal[2],int who); 22. void dealerGetsCard(int *numCards,int cards[52], 23. int dealerPoints[2]); 24. void playerGetsCard(int *numCards,int cards[52], 25. int playerPoints[2]); 26. char getAns(char mesg[]); 27. void findWinner(int total[2]); 28. 29. main() 30. { 31. int numCards; 32. int cards[52],playerPoints[2],dealerPoints[2],total[2]; 33. char ans; 34. 35. do 36. { 37. initCardsScreen(cards,playerPoints,dealerPoints,total, &numCards); 38. dealerGetsCard(&numCards,cards, dealerPoints); 39. printf("\n"); 40. playerGetsCard(&numCards,cards,playerPoints); 41. playerGetsCard(&numCards,cards,playerPoints); 42. do 43. { 44. ans = getAns("Hit or stand (H/S)?"); 45. if ( ans == 'H' ) 46. { 47. playerGetsCard(&numCards,cards,playerPoints); 48. } 49. } 50. while( ans != 'S' ); 51. 52. totalIt(playerPoints,total,PLAYER); 53. do 54. { 55. dealerGetsCard(&numCards,cards,dealerPoints); 56. } 57. while (dealerPoints[ACEHIGH] < 17 ); 58. 59. totalIt(dealerPoints,total,DEALER); 60. findWinner(total); 61. 62. ans = getAns("\nPlay again(Y/N)?"); 63. } 64. while(ans=='Y'); 65. 66. return 0; 67. } 68. 69. void initCardsScreen( int cards[52],int playerPoints[2], 70. int dealerPoints[2], int total[2], 71. int *numCards ) 72. { 73. int sub,val = 1 ; 74. char firstName[15]; 75. *numCards=52; 76. 77. for(sub=0;sub<=51;sub++) 78. { 79. val = (val == 14) ? 1 : val; 80. cards[sub] = val; 81. val++; 82. } 83. 84. for(sub=0;sub<=1;sub++) 85. { 86. playerPoints[sub]=dealerPoints[sub]=total[sub]=0; 87. } 88. dispTitle(); 89. 90. if (askedForName==0) 91. { 92. printf("What is your first name?"); 93. scanf(" %s",firstName); 94. askedForName=1; 95. printf("Ok, %s,get ready for casino action!\n\n",firstName); 96. getchar(); 97. } 98. return; 99. } 100. 101. void playerGetsCard(int *numCards,int cards[52],int playerPoints[2]) 102. { 103. int newCard; 104. newCard = dealCard(numCards, cards); 105. printf("You draw:"); 106. dispCard(newCard,playerPoints); 107. } 108. 109. 110. void dealerGetsCard(int *numCards,int cards[52],int dealerPoints[2]) 111. { 112. int newCard; 113. newCard = dealCard(numCards,cards); 114. printf("The dealer draws:"); 115. dispCard(newCard,dealerPoints); 116. } 117. 118. int dealCard(int * numCards,int cards[52]) 119. { 120. int cardDrawn,subDraw; 121. time_t t; 122. srand(time(&t)); 123. subDraw = (rand()%(*numCards)); 124. cardDrawn = cards[subDraw]; 125. cards[subDraw] = cards[*numCards -1]; 126. (*numCards)--; 127. return cardDrawn; 128. } 129. 130. void dispCard(int cardDrawn, int points[2]) 131. { 132. switch(cardDrawn) 133. { 134. case(11): printf("%s\n","Jack"); 135. points[ACELOW] += 10; 136. points[ACEHIGH] += 10; 137. break; 138. case(12): printf("%s\n","Queen"); 139. points[ACELOW] += 10; 140. points[ACEHIGH] += 10; 141. break; 142. case(13): printf("%s\n","King"); 143. points[ACELOW] += 10; 144. points[ACEHIGH] += 10; 145. break; 146. default : points[ACELOW] += cardDrawn; 147. if(cardDrawn==1) 148. { 149. printf("%s\n","Ace"); 150. points[ACEHIGH]+= 11; 151. } 152. else 153. { 154. points[ACEHIGH]+=cardDrawn; 155. printf("%d\n",cardDrawn); 156. } 157. } 158. return ; 159. } 160. 161. void totalIt(int points[2],int total[2],int who) 162. { 163. if ( (points[ACELOW] == points[ACEHIGH]) 164. ||(points[ACEHIGH] < 21 )) 165. { 166. total[who] = points[ACELOW]; 167. } 168. else 169. { 170. total[who] = points[ACEHIGH]; 171. } 172. 173. if (who == PLAYER ) 174. { 175. printf("You have a total of %d\n\n", total[PLAYER]); 176. } 177. else 178. { 179. printf("The house stands with a total of %d\n\n", 180. total[DEALER]); 181. } 182. return; 183. } 184. 185. void findWinner(int total[2]) 186. { 187. if ( total[DEALER] == 21 ) 188. { 189. printf("The house wins.\n"); 190. return ; 191. } 192. if ( (total[DEALER] > 21) && (total[PLAYER] > 21) ) 193. { 194. printf("%s", "Nobody wins.\n"); 195. return ; 196. } 197. if ((total[DEALER] >= total[PLAYER])&& (total[DEALER] < 21)) 198. { 199. printf("The house wins.\n"); 200. return ; 201. } 202. printf("%s%c","You win!\n",BELL); 203. return; 204. } 205. 206. char getAns(char mesg[]) 207. { 208. char ans; 209. printf("%s", mesg); 210. ans = getchar(); 211. getchar(); 212. return toupper(ans); 213. } 214. 215. void dispTitle(void) 216. { 217. int i = 0 ; 218. while(i<25) 219. { 220. printf("\n"); 221. i++; 222. } 223. printf("\n\n*Step right up to the Blackjack tables*\n\n"); 224. return ; 225. }
main()函数中player完成抽牌之后,立刻计算了player的点数:
52. totalIt(playerPoints,total,PLAYER);
这个计算结果基于ACE的点数被作为1或11两种可能性,取最好一种作为最后的结果。
161. void totalIt(int points[2],int total[2],int who) 162. { 163. if ( (points[ACELOW] == points[ACEHIGH]) 164. ||(points[ACEHIGH] > 21 )) 165. { 166. total[who] = points[ACELOW]; 167. } 168. else 169. { 170. total[who] = points[ACEHIGH]; 171. } 172. 173. if (who == PLAYER ) 174. { 175. printf("You have a total of %d\n\n", total[PLAYER]); 176. } 177. else 178. { 179. printf("The house stands with a total of %d\n\n", 180. total[DEALER]); 181. } 182. return; 183. }
这个函数让我们得以领略什么叫思路含糊和废话连篇。首先
163. if ( (points[ACELOW] == points[ACEHIGH]) 164. ||(points[ACEHIGH] > 21 )) 165. { 166. total[who] = points[ACELOW]; 167. } 168. else 169. { 170. total[who] = points[ACEHIGH]; 171. }
它的意思是当较高点数超过21点时把较低作为最终的点数,否则把较高点数作为最后的点数。显而易见这可以更简洁地表述为
if ( points[ACEHIGH] > 21 ) { total[who] = points[ACELOW]; } else { total[who] = points[ACEHIGH]; }
原来的代码把“(points[ACELOW] == points[ACEHIGH])||”写出来是思路不清导致的拖泥带水。
更简洁的写法是:
total[who] = ( points[ACEHIGH] > 21 )? points[ACELOW]: points[ACEHIGH];
“?:”这个三目运算在这里应用得恰到好处。
有些人对三目运算有一种无名的恐惧,鼓吹所谓“尽量不要用三目运算符”。这是毫无道理的,这种无理源自无知。他们自己不会用刀,于是就骗人骗己地宣称使用木棍强于用刀。
173. if (who == PLAYER ) 174. { 175. printf("You have a total of %d\n\n", total[PLAYER]); 176. } 177. else 178. { 179. printf("The house stands with a total of %d\n\n", 180. total[DEALER]); 181. }
这一段同样拖泥带水,其实它的效果和下面写法没有本质区别:
printf( "%s a total of %d\n\n", who == PLAYER ? "You have" : "The house stands with", total[who] );
所以totalIt()函数应改写为
void totalIt(int [],int [],int ); void totalIt(int points[],int total[],int who) { total[who] = ( points[ACEHIGH] > 21 )? points[ACELOW]: points[ACEHIGH]; printf( "%s a total of %d\n\n", who == PLAYER ? "You have" : "The house stands with", total[who] ); }
计算了完player的点数之后,按照规则在main()中由dealer继续抽牌(前面已抽过第一张牌)。dealer抽牌的策略是不到17点则继续,据代码作者说现实中的庄家的策略也是如此。
53. do 54. { 55. dealerGetsCard(&numCards,cards,dealerPoints); 56. } 57. while ( dealerPoints[ACEHIGH] < 17 );
dealerGetsCard ()函数的功能与playerGetsCard()函数重叠,前面已经提到过,甚至可以说这两个函数都是多余的。
此外这里还有一个更严重的问题,那就是“dealerPoints[ACEHIGH] < 17”这个表达式的逻辑问题。这个表达式要求dealer的点数达到17点或以上时停止抽牌,但问题在于点数有两种计算方法,一种是把Ace作为11点(Soft hand),另一种是把Ace作为1点。“dealerPoints[ACEHIGH] ”的意义是Soft hand点数,但是原作者在对程序的说明中压根就没有明确dealer的Soft hand点数达到或超过17点时停牌,只是泛泛地说了一句“the dealer stands on 17”。按软件工程的说法,这叫需求不清,是比代码错误更加严重的错误。
紧接着,矛盾出现了。
59. totalIt(dealerPoints,total,DEALER);
totalIt()函数计算dealer的点数却是按照最好成绩计算的,这就发生了矛盾。比如dealer为15点时又取了一张牌Ace,按照Soft hand规则,dealer的点数是25点,但最后的成绩却是按照硬牌规则为16点,而如果dealer的点数为16点,那么前面他根本就不应该停牌。这是“双重标准”的C语言版。
这里较为合理的写法应该是
do { dealerGetsCard(&numCards,cards,dealerPoints); totalIt(dealerPoints,total,DEALER); } while ( total [DEALER] < 17 );