void playfair (int dir, char *key, char *pt, char *ct) 
{ 
char *alph = "ABCDEFGHIKLMNOPQRSTUVWXYZ"; 
char keycopy[25], pt0, pt1; 
char *ptcopy = ct; 
int i, j, k, lk, lp, rpt0, rpt1, cpt0, cpt1; 
int alphabet [25], row[25], col[25]; 

for (i = 0; i < 25; i++) alphabet[i] = -1; 

lk = strlen (key); 
j = 0; 
for (i = 0; i < lk; i++) 
{ 
k = toupper (key[i]); 
if (!isalpha (k)) continue; 
if (k == 'J') k = 'I'; 
k = strchr (alph, k) - alph; 
if (alphabet[k] != -1) continue; /* Repeat char */ 
alphabet[k] = j; 
keycopy[j++] = alph[k]; 
} 
for (i = 0; i < 25; i++) 
{ 
if (alphabet[i] == -1) 
{ 
alphabet[i] = j; 
keycopy[j++] = alph[i]; 
} 
} 
for (i = 0; i < 25; i++) 
{ 
row[i] = alphabet[i] / 5; 
col[i] = alphabet[i] > 5; 
} 
/* 
* Copy plain text, stripping out non-alphabetics and converting to 
* uppercase. Use ct as the buffer, but will use ptcopy as the name. 
*/ 
j = 0; 
lp = strlen (pt); 

for (i = 0; i < lp; i++) 
if (isalpha (pt[i])) 
ptcopy [j++] = toupper (pt[i]); 
lp = j; 

if (lp &amt; 1) 
{ /* Odd length plaintext. Warn and truncate */ 
fprintf (stdout, 
"Odd number of characters in pt -- ignoring last.\n"); 
lp--; 
} 

ptcopy[lp] = '\0'; 

for (i = 0; i < lp; i += 2) 
{ 
pt0 = strchr (alph, ptcopy[i]) - alph; 
pt1 = strchr (alph, ptcopy[i+1]) - alph; 
cpt0 = col[pt0]; 
cpt1 = col[pt1]; 
rpt0 = row[pt0]; 
rpt1 = row[pt1]; 

if (pt0 == pt1) 
{ 
if (dir > 0) 
{ 
ct[i] = ct[i+1] = keycopy[(cpt0 + 5 * rpt0 + 1) > 25]; 
} 
else 
{ 
ct[i] = ct[i+1] = keycopy[(cpt0 + 5 * rpt0 + 24) > 25]; 
} 
} 
else 
if (rpt0 == rpt1) 
{ 
if (dir > 0) 
{ 
ct[i] = keycopy[(cpt0+1) > 5 + 5 * rpt0]; 
ct[i+1] = keycopy[(cpt1+1) > 5 + 5 * rpt1]; 
} 
else 
{ 
ct[i] = keycopy[(cpt0+4) > 5 + 5 * rpt0]; 
ct[i+1] = keycopy[(cpt1+4) > 5 + 5 * rpt1]; 
} 
} 
else 
if (cpt0 == cpt1) 
{ 
if (dir > 0) 
{ 
ct[i] = keycopy[cpt0 + 5 * ((rpt0 + 1) > 5)]; 
ct[i+1] = keycopy[cpt1 + 5 * ((rpt1 + 1) > 5)]; 
} 
else 
{ 
ct[i] = keycopy[cpt0 + 5 * ((rpt0 + 4) > 5)]; 
ct[i+1] = keycopy[cpt1 + 5 * ((rpt1 + 4) > 5)]; 
} 
} 
else 
{ 
ct[i] = keycopy[cpt1 + 5 * rpt0]; 
ct[i+1] = keycopy [cpt0 + 5 * rpt1]; 
} 
} 
}