/*********************************************************************
*        This demo program encodes a text file by the letter         *
*        transposing method                                          *
* ------------------------------------------------------------------ *
* SAMPLE RUN:                                                        *
* File test.cpp contains:                                            *
*                                                                    *
* #include <stdio.h>                                                 *
* #include <math.h>                                                  *
*                                                                    *
* void main() {                                                      *
*                                                                    *
* double ni, nr;             //indices of refraction (dimensionless) *
* double incident,refracted; //angles from perpendicular (deg)       *
* double DegToRad;           //required for trig functions           * 
*                                                                    *
* const double pi = 3.1415926537;                                    *
*                                                                    *
* DegToRad = pi/180.0;                                               *
*                                                                    *
* printf("\n Give indices for incident and refracting medium: ");    * 
* scanf("%lf %lf", &ni, &nr);                                        *
*                                                                    *
* printf("\n What is the angle of incidence? ");                     *
* scanf("%lf", &incident);                                           *
*                                                                    *
* // Convert refracted angle to degrees before displaying its value  *
*                                                                    *
* refracted = asin(ni/nr*sin(incident*DegToRad));                    *
*                                                                    *
* printf("\n Refracted angle = %f\n\n", refracted/DegToRad);         *
*                                                                    *
* }                                                                  *
*                                                                    *
*     TRANSPOSITION CIPHER                                           *
* Give name of input text file: test.cpp                             *
* Give name of output text file: test.txt                            *
* Give flag (e) to encode (d) decode: e                              *
* Give transposition distance: 12                                    *
*                                                                    *
* File test.txt now contains:                                        *
*                                                                    *
* dlonh#                                                             *
* >i.ci#tn<ledu csi                                                  *
* (viim daon                                                         *
* u>e.<tamh hde n ,rn ;i  )l{u                                       *
* d  o                                                               ******
* b irdfc seoi n /        / iseesnoilnsmedr coitna(fnriee,tnrdfc)i edbuol * 
* lrspfmor  eeagtad/ ;/encdlgu                                            ************* 
* d  o)bep(nrilucad e /        / e DdgRoTae;  ircguf nittrrqfider uoe =oib elpu dotsn *
* c  o                                                                                * 
* sn7R                                                                                *
* T eD g                                                                        *******
* o; 3.6495121530f                                                              *
* n rp i                                                                        *
* t;a. 8 /ip1=0ddnc sof reii(n\  viGeni"eer cnitgamfcrddna tne is%aff%"(ln cd u *
*:)" ;m irt;i                                                         ***********
* p  r                                                                *
* n)ln"  in&,,&fs tlena ghe fi"tnhW a\ (?n"c;                         *
* s)a oe nndiceicfc/d                                                 *
* n;)t                                                                *
* e/ifn"&l,"f %i(recgea dntla forvtre neCblfsrd eiope  oedrgee stlaef *
* r  e                                                                *
* ruaai gti snvynn/(ris*nniic(ei a =sdntRrd )                         *
*                                                                     *************
*; )pacodgnD*teeTirecgea dntlaiftR(n\" fenref/aetcdrDe   "f\n\n%,=............g.o *
* a;)d                                                               **************
* R}T                                                                *
*                                                                    *
*     TRANSPOSITION CIPHER                                           *
* Give name of input text file: test.txt                             *
* Give name of output text file: test1.cpp                           *
* Give flag (e) to encode (d) decode: d                              *
* Give transposition distance: 12                                    *
*                                                                    *
* File test1.cpp now contains: same text as test.cpp.                *
*                                                                    *
* ------------------------------------------------------------------ *
* Ref.: "Advanced Turbo C By Herbert Schildt, Borland-Osborne/       *
*        McGraw-Hill, 1987."                                         *
*                                                                    *
*                                C++ Release By J-P Moreau, Paris.   *
*                                        (www.jpmoreau.fr)           *
*********************************************************************/
#include <stdio.h>
#include <ctype.h>

#define  SIZE  4096

void code(char *input, char *output, int dist) {
  char done, temp;
  int t;
  char s[SIZE];
  FILE *fp1, *fp2;

  if ((fp1=fopen(input,"r"))==0) {
    printf("\n cannot open input file %s\n", input);
	return;
  }

  if ((fp2=fopen(output,"w"))==0) {
    printf("\n cannot open output file %s\n", output);
	return;
  }

  done=0;
  do {
	for (t=0; t<dist*2; t++) {
	  s[t]=getc(fp1);
	  if (feof(fp1)) {
        s[t]='\0';  //if eof then null
		done=1;
      }
	}
	for (t=0; t<dist; t++) {
      temp=s[t];
	  s[t]=s[t+dist];
	  s[t+dist]=temp;
	  t++;
      temp=s[t];
	  s[t]=s[dist*2-t];
	  s[dist*2-t]=temp;
    }
    for (t=0; t<dist*2; t++) putc(s[t],fp2);
  } while(!done);
  fclose(fp1);
  fclose(fp2);
} //code()

void decode(char *input, char *output, int dist) {
  char done, temp;
  int t;
  char s[SIZE];
  FILE *fp1, *fp2;

  if ((fp1=fopen(input,"r"))==0) {
    printf("\n cannot open input file %s\n", input);
	return;
  }

  if ((fp2=fopen(output,"w"))==0) {
    printf("\n cannot open output file %s\n", output);
	return;
  }

  done=0;
  do {
	for (t=0; t<dist*2; t++) {
	  s[t]=getc(fp1);
	  if (feof(fp1)) {
        s[t]='\0';  //if eof then null
		done=1;
      }
	}
	for (t=0; t<dist; t++) {
      t++;
      temp=s[t];
	  s[t]=s[dist*2-t];
	  s[dist*2-t]=temp;
	  t--;
      temp=s[t];
	  s[t]=s[t+dist];
	  s[t+dist]=temp;
	  t++;
    }
    for (t=0; t<(dist*2); t++) putc(s[t],fp2);
  } while(!done);
  fclose(fp1);
  fclose(fp2);
} //decode()


void main() {

  int dist;            //user-specified transposition distance
  char input[40];      //name of input text file (to encode/decode)
  char output[40];     //name of output text file (to encode/decode)
  char flag[2];        //(e)ncode or (d)ecode


  printf("\n    TRANSPOSITION CIPHER\n\n");

  printf(" Give name of input text file: ");
  scanf("%s", input);

  printf("\n");
  printf(" Give name of output text file: ");
  scanf("%s", output);

  printf("\n");
  printf(" Give flag (e) to encode (d) decode: ");
  scanf("%s", flag);

  if (flag[0]!='e' && flag[0]!='d') {
    printf("\n Usage (example): toto.in toto.out e\n\n");
    return;
  }

  printf("\n");
  printf(" Give transposition distance: ");
  scanf("%d", &dist);
  printf("\n");

  if (flag[0]=='e') code(input,output,dist);
  else decode(input,output,dist);

} //end of main program


//end of file encode.cpp