ENCRYPTION IN UNIX C

ENCRYPTION

[ragava@localhost ~]$ cat ec.c
#include<stdio.h>

main(int argc, char *argv[])
        {
                int i;
                char a[2000],b;
                FILE *fp;
                if(argc!=2)
                        {
                                printf("Usage error");
                                return;
                        }

                fp=fopen(argv[1],"r");
                if(fp==NULL)
                        {
                                printf("ERROR IN OPENING A FILE");
                                return;
                        }
                for(i=0,a[i]=getc(fp);feof(fp)!=0;a[++i]=getc(fp))
                                 ;
                a[i]='\0';
                fclose(fp);
                remove(argv[1]);
                fp=fopen(argv[1],"w");

                for(i=0;a[i]!='\0';i++)

                        {
                                b=a[i]+2;
                                putc(b,fp);
                        }
                fclose(fp);
        }