Encode_Decode [Complete]

/*  Author: Leandro Soares
    School: INETE
    Date:   19-03-2012
    Time:   20:19   */

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <ctype.h>
#include <string.h>

#define maxRuns 13
#define ENC "Encode"
#define DEC "Decode"

char Menu_Geral(void);
void Ask_Fname(char *sname);
char Encode_Letter(char letter, char type[]);
void code_file(char *fname, char type[]);
void Add_ext(char *sname);

int main(void) {
    char option_MG, option, sname[20];
    char test;

    sname[0] = '\0';
    option_MG = option = '\0';

    while( option_MG != 'e' ) {
        option_MG = Menu_Geral();

        if( option_MG == 'q' ) {
            Ask_Fname(sname);
            code_file(sname, ENC);
        }
        else    if( option_MG == 'w' ) {
            Ask_Fname(sname);
            code_file(sname, DEC);
        }
    }

    return 0;
}

char Menu_Geral(void) {
    char option = '\0';

    system("cls");
    printf("\t\tMenu Geral\n\n");
    printf("\tq - Encode\n");
    printf("\tw - Decode\n");
    printf("\te - Sair\n\n");

    while( option != 'q' && option != 'w' && option != 'e' ) {
        fflush(stdin);
        option = getch();
    }
    fflush(stdin);

    return option;
}

void Ask_Fname(char *sname) {
    system("cls");
    printf("Nome do ficheiro: ");
    gets(sname);
}
char Encode_Letter(char letter, char type[]) {
    int idxa, idxb;
    char min, max;

    if( ( letter >= 'a' && letter <= 'z' ) || ( letter >= 'A' && letter <= 'Z' ) ) {
        if( islower(letter) ) {
            min = 'a';
            max = 'z';
        }
        else    if ( isupper(letter) ){
            min = 'A';
            max = 'Z';
        }

        for(idxb = maxRuns, idxa = letter; idxb > 0 ; idxb--, idxa++) {
            if( idxa == max )
                idxa = min-1;
        }

        letter = idxa;
    }
    else
        letter = '\0';

    return letter;
}
void code_file(char *fname, char type[]) {
    FILE * pFileE, *pFileOutput;
    char strbuffer[5000], strbufferOUT[5000];
    int idx = 0;

    strbufferOUT[0] = strbuffer[0] = '\0';

    Add_ext(fname);
    pFileE = fopen(fname,"r");
    if( !strcmp(type, DEC) )
        pFileOutput = fopen("decoded.txt", "w");
    if( !strcmp(type, ENC) )
        pFileOutput = fopen("encoded.txt", "w");

    while( fgets(strbuffer,4997,pFileE) != NULL ){
        while( strbuffer[idx] != '\0' ) {
            if( ( strbuffer[idx] >= 'a' && strbuffer[idx] <= 'z' ) || ( strbuffer[idx] >= 'A' && strbuffer[idx] <= 'Z' ) )
                strbufferOUT[idx] = Encode_Letter(strbuffer[idx], type);
            else
                strbufferOUT[idx] = strbuffer[idx];
            idx++;
        }
        strbufferOUT[idx] = '\0';
        fputs(strbufferOUT, pFileOutput);
        idx = 0;
    }
    system("cls");
    if( !strcmp(type, DEC) )
        printf("Descodificacao completa!!\n\n");
    if( !strcmp(type, ENC) )
        printf("Codificacao completa!!\n\n");
    system("pause");

    fclose(pFileOutput);
    fclose(pFileE);
}
void Add_ext(char *sname) {
    while( *sname != '\0' ) sname++;
    *(sname) = '.';
    *(sname+1) = 't';
    *(sname+2) = 'x';
    *(sname+3) = 't';
    *(sname+4) = '\0';
}