Article · October 008 citations reads 5,930 authors

Listing One
// bkadd
#include
#include
#include
#include
#define MAX_WORD_LEN 100
int main(int argc, char *argv[])
{
FILE *fp_cod, *fp_book;
int ch, charno;
char word[MAX_WORD_LEN];
int fromstart = 1;
int wlen = 0;
// Argument processing
char code[_MAX_PATH], book[_MAX_PATH];
char drive[_MAX_DRIVE];
char dir[_MAX_DIR];
char fname[_MAX_FNAME];
char ext[_MAX_EXT];
if (argc != 3 && argc != 4) goto error1;
_splitpath(argv[1], drive, dir, fname, ext );
if (strlen(ext) == 0) strcpy(ext, "cod");
_makepath(code, drive, dir, fname, ext);
_splitpath(argv[2], drive, dir, fname, ext );
if (strlen(ext) == 0) strcpy(ext, "txt");
_makepath(book, drive, dir, fname, ext);
if (argc == 3 ||(sscanf(argv[3], "%d", &charno) != 1)
|| (charno == 0)) charno=1;
if (charno < 0) { fromstart = 0; charno = -charno; }
// File opening
if ((fp_cod = fopen(code, "a")) == NULL) goto error2;
if ((fp_book = fopen(book, "r")) == NULL) goto error3;
// Main loop
do {
ch = getc(fp_book);
if (isalpha(ch))
word[wlen++] = ch;
else {
if (charno <= wlen)
putc(toupper(word[fromstart ?
(charno - 1) : (wlen - charno)]), fp_cod);
wlen = 0;
}
} while (!feof(fp_book));
// Termination
fclose(fp_book); fclose(fp_cod); return 0;
// Error handling
error1: printf("USAGE: bkadd codfile bookfile [charno]\n"); return 1;
error2: printf("Can not open code file %s\n", argv[1]); return 1;
error3: fclose(fp_cod);
printf("Can not open book file %s\n", argv[2]); return 1;
}
Plaintext
D 
R 
D 
O
B 
B
S
Plaintext 
(hex) 
44 52 44
4F 42
42
53
Running key
H
E
R 
M
I 
O 
N
Running key (hex)
48 
45 
52 
4D
49
4F 
4E
Ciphertext 
(hex)
0C 17 16 02 0B 0D
1D
Ciphertext
12 
23 
22 
2 
11 
13 
29