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问题:
据说最早的密码来自于罗马的凯撒大帝。消息加密的办法是:对消息原文中的每个字母,分别用该字母之后的第5个字母替换(例如:消息原文中的每个字母A都分别替换成字母F)。而你要获得消息原文,也就是要将这个过程反过来。
密码字母:A B C D E F G H I J K L M N O P Q R S T U V W X Y Z M
原文字母:V W X Y Z A B C D E F G H I J K L M N O P Q R S T U
(注意:只有字母会发生替换,其他非字母的字符不变,并且消息原文的所有字母都是大写的。)
输入:最多不超过100个数据集组成,每个数据集之间不会有空行,每个数据集由3部分组成:
1. 起始行:START
2. 密码消息:由1到200个字符组成一行,表示凯撒发出的一条消息.
3. 结束行:END
在最后一个数据集之后,是另一行:ENDOFINPUT。
输出:
每个数据集对应一行,是凯撒的原始消息。
n Sample Input
START
NS BFW, JAJSYX TK NRUTWYFSHJ FWJ YMJ WJXZQY TK YWNANFQ HFZXJX
END
START
N BTZQI WFYMJW GJ KNWXY NS F QNYYQJ NGJWNFS ANQQFLJ YMFS XJHTSI NS WTRJ
END
START
IFSLJW PSTBX KZQQ BJQQ YMFY HFJXFW NX RTWJ IFSLJWTZX YMFS MJ
END
ENDOFINPUT
n Sample Output
IN WAR, EVENTS OF IMPORTANCE ARE THE RESULT OF TRIVIAL CAUSES
I WOULD RATHER BE FIRST IN A LITTLE IBERIAN VILLAGE THAN SECOND IN ROME
DANGER KNOWS FULL WELL THAT CAESAR IS MORE DANGEROUS THAN HE
代码:
#include <stdio.h>#include <stdlib.h>#include <ctype.h>#include <string.h>#define MAXLINE 1000void decipher(const char *cipher, char *text);int main(int argc, char *argv[]){ FILE *fin = fopen("intext.txt", "r"); FILE *fout = fopen("outtext.txt", "w"); if(fin == NULL || fout == NULL) return EXIT_FAILURE; char line[MAXLINE+1] = ""; char text[MAXLINE+1] = ""; while (fgets(line, MAXLINE, fin) != NULL) { if (strcmp(line, "START\n") == 0) { fgets(line, MAXLINE, fin); printf("%s", line);getchar(); decipher(line, text); fprintf(fout, "%s", text); if (fgets(line, MAXLINE, fin) == NULL) perror("fgets error"); if (strcmp(line, "END\n") != 0) { printf("not match END\n"); return EXIT_FAILURE; } } else if (strcmp(line, "ENDOFINPUT") == 0) { printf("cophertext is end\n"); return EXIT_SUCCESS; } else { printf("unknow text\n"); return EXIT_FAILURE; } } return 0;}void decipher(const char *cipher, char *text){ size_t j = 0; for (size_t i = 0; cipher[i] != '\0'; ++i) { if (isupper(cipher[i])) { if (cipher[i] >= 'E') text[j++] = cipher[i] - 5; else text[j++] = 'Z' - (4 - (cipher[i] - 'A')); } else { text[j++] = cipher[i]; } } text[j] = '\0';}
输入文件是:intext.txt
START NS BFW, JAJSYX TK NRUTWYFSHJ FWJ YMJ WJXZQY TK YWNANFQ HFZXJXENDSTART N BTZQI WFYMJW GJ KNWXY NS F QNYYQJ NGJWNFS ANQQFLJ YMFS XJHTSI NS WTRJENDSTART IFSLJW PSTBX KZQQ BJQQ YMFY HFJXFW NX RTWJ IFSLJWTZX YMFS MJENDENDOFINPUT
输出文件是:outtext.txt
IN WAR, EVENTS OF IMPORTANCE ARE THE RESULT OF TRIVIAL CAUSES I WOULD RATHER BE FIRST IN A LITTLE IBERIAN VILLAGE THAN SECOND IN ROME DANGER KNOWS FULL WELL THAT CAESAR IS MORE DANGEROUS THAN HE