/****************************************************************** * Programmer

Question

/******************************************************************
* Programmer: Roland
*
* Date: April 12, 2012
*
*
* File name: myMain.cpp
*
* Description: Demonstrates basic cin, cout, selection structures, IO manipulation
* and formatting, user-defined functions, array processing, cstring,
* string, file input and output.
*
* Assumptions: Assumes that the user enters an encryption key of upto 128 characters
* that are all lower case. It also assumes the user enters a file name.
*
* Input: keyboard - 128 lower case characters, file name.
*
* Output: screen - Decrypted file.
*
*
********************************************************************/


#include <iostream> //header files
#include <iomanip>
#include <string>
#include <cstring>
#include <fstream>

using namespace std;



string ende[]={"encrypt","decrypt"},buffer,key,newbuffer="";

char filename[80],enmap[128],demap[128],again;

int i,maplength;

char ch;

bool stop = false;


void creatfile ();

void displayMenu (); //function prototypes

void getMenuSelection (char ch);

void getFileName ();

void getKey ();

void EncryptionMap (string,char[]);

void DencryptionMap (string,char[]);

void Encryption (const string,const char[],int,string&);



int main ()

{

creatfile (); //creates a file to encrypt


extern bool stop;



while (!stop) //main program continuous loop that will display menu

{

displayMenu();

cin >> ch;

getMenuSelection (ch);


}

return 0;

}


void creatfile () //function creates file
{
ofstream file;
file.open ("myfile.txt");
file << "This is my file line 1 ";
file << "I have written line two ";
file << "my file line three ";
file << "how many lines do I have to write? ";
file << "This is line five now. ";
file << "My fingers are tired! ";
file << "S E V E N ";
file << "I ate line eight. ";
file << "Almost there. ";
file << "This is my favorite line, number 10!";


file.close();

cout << "file has been written!";

}


void displayMenu () //displays menu options

{

cout << " Do you want to perform a file Encryption or Decryption? Choose an option:" << endl

<< "E for Encryption" << endl

<< "D for Decryption" << endl

<< "Q to quit." << endl;

}



void getMenuSelection (char ch) //switch statement nested in void function

{

extern bool stop;



switch (ch)

{

case 'e':

case 'E':

getFileName ();

getKey ();

EncryptionMap (key, enmap);

Encryption (buffer,demap,maplength,newbuffer);

break;

case 'd':

case 'D':

getFileName ();

getKey ();

DencryptionMap (key,demap);

Encryption (buffer,demap,maplength,newbuffer);


break;

case 'q':

case 'Q':

stop = true;

break;

default:

cout << "Invalid selection. Try again." << endl;

stop = false;

}

}

void getFileName ()

{

ofstream out;

ifstream in;

cout<<"Enter name of your file to manipulate : ";

cin>>filename;

in.open(filename);

if(in.fail())

{
cout<<"input file did not open please check it ";

system("pause");
}

else

cout<<"Enter name of your output file: ";

cin>>filename;

out.open(filename);


}

void getKey () //void function that sends encryption/decryption key characters

{

cout<<"Insert your encryption key (max 128 characters): ";

cin>>key;

if(key.length()>128)
{

cout<<"key too long ";

cout<<"Enter your encryption key (max 128 characters): ";

cin>>key;

}

maplength=key.length();


}

void EncryptionMap (string key,char map[]) // Encrypts the file

{

int i;

for(i=0;i<key.length();i++)

map[i]=key[i]-'a';

}

void DecryptionMap (string key,char map[]) // decrypts then encrypted file

{

int i;

for(i=0;i<key.length();i++)

map[i]=26-(key[i]-'a');

}

void Encryption (const string buffer,const char map[],int len,string& newbuffer)

{

int i=0;

char t,code;

for(i=0;i<buffer.length();i++)

{
cout<<buffer[i]<<" "<<i<<endl;

if(isalpha(buffer[i]))

{if(islower(buffer[i]))

code='a';

else

code='A';

t=buffer[i]-code;

cout<<code<<" "<<buffer[i]<<" "<<t<<" "<<i<<endl;

t=t+map[i%len];

t=t%26;

t=t+code;

newbuffer.push_back(t);

}

else

newbuffer.push_back(buffer[i]);

}

newbuffer.push_back(' ');
}

Explanation / Answer

#include "stdafx.h" #include //header files #include #include #include #include using namespace std; string ende[]={"encrypt","decrypt"},buffer,key,newbuffer=""; char filename[80],enmap[128],demap[128],again; int i,maplength; char ch; bool stop = false; void creatfile (); void getFileName (); void getKey (); void EncryptionMap (string,char[]); void DencryptionMap (string,char[]); void Encryption (const string,const char[],int,string&); void displayMenu (); //function prototypes void getMenuSelection (char ch); int main () { creatfile (); //creates a file to encrypt extern bool stop; while (!stop) //main program continuous loop that will display menu { displayMenu(); cin >> ch; getMenuSelection (ch); } return 0; } void creatfile () //function creates file { ofstream file; file.open ("myfile.txt"); file

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