第二章 基本概念 [c和指针]

 代码风格和规范有多么重要？看看本章中所列入的例程就明白了。

例程2-1

#include <stdio.h>main(t,_,a)char *a;{return!0<t?t<3?main(-79,-13,a+main(-87,1-_,main(-86, 0, a+1 )+a)):1,t<_?main(t+1, _, a ):3,main ( -94, -27+t, a)&&t == 2 ?_<13 ?main ( 2, _+1, "%s %d %d\n" ):9:16:t<0?t<-72?main(_,t,"@n'+,#'/*{}w+/w#cdnr/+,{}r/*de}+,/*{*+,/w{%+,/w#q#n+,/#{l,+,/n{n+\,/+#n+,/#;#q#n+,/+k#;*+,/'r :'d*'3,}{w+K w'K:'+}e#';dq#'l q#'+d'K#!/\+k#;q#'r}eKK#}w'r}eKK{nl]'/#;#q#n'){)#}w'){){nl]'/+#n';d}rw' i;# ){n\l]!/n{n#'; r{#w'r nc{nl]'/#{l,+'K {rw' iK{;[{nl]'/w#q#\n'wk nw' iwk{KK{nl]!/w{%'l##w#' i; :{nl]'/*{q#'ld;r'}{nlwb!/*de}'c \;;{nl'-{}rw]'/+,}##'*}#nc,',#nw]'/+kd'+e}+;\#'rdq#w! nr'/ ') }+}{rl#'{n' ')# }'+}##(!!/"):t<-50?_==*a ?putchar(a[31]):main(-65,_,a+1):main((*a == '/')+t,_,a\+1 ):0<t?main ( 2, 2 , "%s"):*a=='/'||main(0,main(-61,*a, "!ek;dc \i@bK'(q)-[w]*%n+r3#l,{}:\nuwloca-O;m .vpbks,fxntdCeghiry"),a+1);}

程序输出

On the first day of Christmas my true love gave to mea partridge in a pear tree.On the second day of Christmas my true love gave to metwo turtle dovesand a partridge in a pear tree.On the third day of Christmas my true love gave to methree french hens, two turtle dovesand a partridge in a pear tree.On the fourth day of Christmas my true love gave to mefour calling birds, three french hens, two turtle dovesand a partridge in a pear tree.On the fifth day of Christmas my true love gave to mefive gold rings;four calling birds, three french hens, two turtle dovesand a partridge in a pear tree.On the sixth day of Christmas my true love gave to mesix geese a-laying, five gold rings;four calling birds, three french hens, two turtle dovesand a partridge in a pear tree.On the seventh day of Christmas my true love gave to meseven swans a-swimming,six geese a-laying, five gold rings;four calling birds, three french hens, two turtle dovesand a partridge in a pear tree.On the eighth day of Christmas my true love gave to meeight maids a-milking, seven swans a-swimming,six geese a-laying, five gold rings;four calling birds, three french hens, two turtle dovesand a partridge in a pear tree.On the ninth day of Christmas my true love gave to menine ladies dancing, eight maids a-milking, seven swans a-swimming,six geese a-laying, five gold rings;four calling birds, three french hens, two turtle dovesand a partridge in a pear tree.On the tenth day of Christmas my true love gave to meten lords a-leaping,nine ladies dancing, eight maids a-milking, seven swans a-swimming,six geese a-laying, five gold rings;four calling birds, three french hens, two turtle dovesand a partridge in a pear tree.On the eleventh day of Christmas my true love gave to meeleven pipers piping, ten lords a-leaping,nine ladies dancing, eight maids a-milking, seven swans a-swimming,six geese a-laying, five gold rings;four calling birds, three french hens, two turtle dovesand a partridge in a pear tree.On the twelfth day of Christmas my true love gave to metwelve drummers drumming, eleven pipers piping, ten lords a-leaping,nine ladies dancing, eight maids a-milking, seven swans a-swimming,six geese a-laying, five gold rings;four calling birds, three french hens, two turtle dovesand a partridge in a pear tree.

不管你是否相信，这竟然是歌曲The twelve Days of Christmas的歌词，而这段代码是Cambridge Consultants Ltd 的 Ian Phillipps编写，用于参加国际C混乱代码大赛。

 

课后练习2-2

/*练习2-2检验输入的花括号是否成对并且合理，以}开始的花括号对是不合理的表现；要求不合理时，提示错误；{多时，打印多出的个数*/#include <stdio.h>#include <stdlib.h>int main(){    int num;    int n = 0;    char ch;    num = 0;    while((ch = getchar()) != NULL){          if(ch == '{')            num += 1;          if(ch == '}'){            if(num == 0)                printf("Error,duo yu de da kuo hu!\n");            else                num -= 1;          }          /*if more than 10 times input,stop checking*/          n++;          if(n>10)            break;     }     if(num > 0)        printf(" duo yu de kuo hu shu: %d \n",num);    return EXIT_SUCCESS;}

这里面我添加了while()退出条件，即if(n > 10) break;书中参考例子中没有这个退出条件，也就是无法退出循环，但因为连回车也寄存在缓冲区了，这里的n将所有输入字符也计算在内了，所以没有达到仅记录花括号的目的。再次阅读getchar函数的实现后发现，这里循环条件的判断和循环体内的计数器并不能同步实现，而是先将输入的字符存在缓存中，等待输入回车后一起返回并循环执行循环体内的语句。

注：

函数名: getchar
功  能: 从stdin流中读字符
用  法: int getchar(void);
注解：
getchar有一个int型的返回值.当程序调用getchar时.程序就等着用户按键.用户输入的字符被存放在键盘缓冲区中.直到用户按回车为止(回车字符也放在缓冲区中).getchar函数的返回值是用户输入的第一个字符的ASCII码,如出错返回-1,且将用户输入的字符回显到屏幕.如用户在按回车之前输入了不止一个字符,其他字符会保留在键盘缓存区中,等待后续getchar调用读取.也就是说,后续的getchar调用不会等待用户按键,而直接读取缓冲区中的字符,直到缓冲区中的字符读完为后,才等待用户按键