Encode_DecodeV2 [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 Encode_Letter(char letter, char type[]);
void code_file(char *fname, char type[]);
void Add_ext(char *sname);
void code_text(char *fnameO);

int main(int argc, char *argv[]) {
    char snameI[20], snameO[20];
    snameI[0] = snameO[0] = '\0';

    if( !strcmp(argv[1], "textencode") && argc == 3) {
        strcpy(snameO, argv[2]);
        code_text(snameO);
    }
    else {
        if( ( strlen(argv[2]) < 20 && strlen(argv[3]) < 20 ) && argc == 4 ) {
            strcpy(snameI, argv[2]);
            strcpy(snameO, argv[3]);

            if( !strcmp(argv[1], "encode")  )
                code_file(snameI, snameO, ENC);
            else    if( !strcmp(argv[1], "decode") )
                code_file(snameI, snameO, DEC);
        }
    }
    return 0;
}

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 *Ofname, char type[]) {
    FILE * pFileE, *pFileOutput;
    char strbuffer[5000], strbufferOUT[5000];
    int idx = 0;

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

    Add_ext(fname);
    Add_ext(Ofname);
    pFileE = fopen(fname,"r");
    if( !strcmp(type, DEC) )
        pFileOutput = fopen(Ofname, "w");
    if( !strcmp(type, ENC) )
        pFileOutput = fopen(Ofname, "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;
    }

    if( !strcmp(type, DEC) )
        printf("\nDescodificacao completa!!\n\tFicheiro de Input: %s \n\tFicheiro de Output: %s \n\n", Ofname, fname);
    if( !strcmp(type, ENC) )
        printf("\n\nCodificacao completa!!\n\tFicheiro de Input: %s \n\tFicheiro de Output: %s \n\n", fname, Ofname);

    fclose(pFileOutput);
    fclose(pFileE);
}
void code_text(char *fnameO) {
    char strbuffer[5000], strbufferOUT[5000];
    int idx = 0;
    FILE *pFileOutput;

    Add_ext(fnameO);
    pFileOutput = fopen(fnameO, "w");

    printf("\n\n>");
    scanf("%[^\n]s", strbuffer);

    while( strbuffer[idx] != '\0' ) {
        if( ( strbuffer[idx] >= 'a' && strbuffer[idx] <= 'z' ) || ( strbuffer[idx] >= 'A' && strbuffer[idx] <= 'Z' ) )
            strbufferOUT[idx] = Encode_Letter(strbuffer[idx], ENC);
        else
            strbufferOUT[idx] = strbuffer[idx];
        idx++;
    }
    strbufferOUT[idx] = '\0';
    fputs(strbufferOUT, pFileOutput);
    idx = 0;

    printf("\nCodificacao completa!!\n\tFicheiro de Output: %s \n\n", fnameO);
    fclose(pFileOutput);
}
void Add_ext(char *sname) {
    while( *sname != '\0' ) sname++;
    *(sname) = '.';
    *(sname+1) = 't';
    *(sname+2) = 'x';
    *(sname+3) = 't';
    *(sname+4) = '\0';
}