Thread: Reading three digits at a time as one number in a long string of numbers

How can I read a file that contains numbers only, but read it by three digits at a time? I have a long string of numbers and every three digits corresponds to a particular number in itself. i.e. a string of 064045154 would need to be read as '064' '045' and '154'. I need to then subtract one from each of these numbers and the new values I need to convert into their ASCII characters and place these in a new file. This is what I have (focusing on the 'Decrypt' function) but all it does is in the new file place a string of the same character repeated over and over a total number of times equal to the number of integers in the numbers file.

Code:

#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "limits.h"


int Encrypt(char * FILENAME)
{
    char NEW_FILENAME[strlen(FILENAME)+4];
    FILE *inFile;   //Declare inFile
    FILE *outFile;  //Declare outFile
    int dpos;
    char *ptr= strrchr(FILENAME, '.');

    dpos=(ptr-FILENAME);
    strncpy(NEW_FILENAME, FILENAME, dpos);
    NEW_FILENAME[dpos] = '\0';
    strcat(NEW_FILENAME, ".enc");

    int Byte;
    char newByte;

inFile = fopen(FILENAME,"rb");
outFile = fopen(NEW_FILENAME, "w");
if(inFile == NULL || outFile == NULL)
    {
        printf("Error in opening file");
        return 1;
    }
else
    {
    printf("\nFile Opened, Encrypting");

    while ( !feof( inFile ) )
    {
        Byte=fgetc(inFile);
        newByte=Byte+1;
        if(newByte<100)
        {
            fprintf(outFile,"0%d",newByte);
        }
        else
        {
            fprintf(outFile,"%d",newByte);
        }
    }

        fclose(inFile);
        fclose(outFile);
    }
return 0;
}

int Decrypt(char * FILENAME)
{
    char NEW_FILENAME[strlen(FILENAME)];
    FILE *inFile;   //Declare inFile
    FILE *outFile;  //Declare outFile
    int dpos;
    char *ptr=strrchr(FILENAME, '.');

    dpos=(ptr-FILENAME);
    strncpy(NEW_FILENAME, FILENAME, dpos);
    NEW_FILENAME[dpos] = '\0';
    strcat(NEW_FILENAME, ".dec");

inFile = fopen(FILENAME,"rb");
outFile = fopen(NEW_FILENAME, "w");

        int newByte;
        int Byte;

    if(inFile == NULL || outFile == NULL)
{
        printf("Error in opening file");
        return 1;
}
    else
{
        printf("\nFile Opened, Decrypting");
}
    while (Byte=fgetc(inFile) != EOF)
{
        char Count[4];

        int i;

           while (i=0, i<3, i++)
{
        Count[i]=fgetc(inFile);
}
        int b=atoi(Count);

        newByte=b-1;


        fprintf(outFile,"%c", newByte);
}

        fclose(inFile);
        fclose(outFile);

return 0;
}

int main(int argc, char*argv[])
{
    if(strcmp(argv[1], "-e") == 0)
    {
        char *file_to_be_enc=argv[2];
        Encrypt(file_to_be_enc);
    }
    else if(strcmp(argv[1], "-d") == 0)
    {
        char *file_to_be_dec=argv[2];
        Decrypt(file_to_be_dec);
    }
    return 0;
}