C语言实现RAS算法示例：简单加密解密程序

/*This is a simple RSA program used in DOS command*/
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
void main(int argc, char *argv[]){
FILE *fileI,*fileO;int iperr=0;unsigned char r,rtemp,r1,r2,calc,*filein,*fileout;
unsigned long bignumber,keynumberin,keynumberout,i,r1l,r2l;
/*Debug code choose 1*/int process=0;
/*Choices:
 bignumber keynumberin keynumberout
 21        5           5
 33        7           3
 35        5           5
 39        5           5
*/
bignumber=33;keynumberin=7;keynumberout=3;
/*Make sure the arguments are + or -*/
if(argc!=4){iperr=1;goto iperr;}
/*Make sure the second argument is + or -.*/
if(!(
(strlen(argv[1])==1)&&(*argv[1]=='+'||*argv[1]=='-'))){iperr=1;goto iperr;}calc=*argv[1];
/*Open source and output files.*/
if((fileI=fopen(argv[2],"rb"))==NULL){printf("Cannot read from %s\n",argv[2]);goto exit;}
if((fileO=fopen(argv[3],"wb"))==NULL){printf("Cannot write to %s\n",argv[3]);goto exit;}goto run;
iperr:
printf("Input \"+\" or \"-\"\n");
getcalc:
calc=getch();if(!(calc=='+'||calc=='-'))goto getcalc;printf("%c",calc);
printf("\nThe input file:");scanf("%s",filein);
if((fileI=fopen(filein,"rb"))==NULL){printf("Cannot read from %s\n",filein);goto exit;}