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#include <iostream>
#include <string>
#include <stdio.h>
#include <ctype.h>
#include <fstream>
#include <sstream>
#include <cstdlib>
using namespace std;
void alpha_to_num(char &ch){
ch -= 'A';
}
void num_to_alpha(int &num){
num += 'A';
}
void encoding (int &c,int p,int k){
c = (p+k)%26;
}
void decoding ( int &c, int p, int k){
if((c-k )<0)
{
p = ((c+26)-k)%26;
}
else
{
p = (c-k)%26;
}
}
int main(){
string keyword;
string plaintext;
int c = 0;
int k;
int p;
int c2;
char action;
k= (int)keyword.length();
p = (int)plaintext.length();
string line;
ifstream myfile ("value.txt");
if (myfile.is_open())
{
while ( getline (myfile,keyword) )
myfile.close();
}
else cout << "Unable to open file.Please rename the key word file as 'value.txt'\n";
cout<< "Enter the message:\n";
getline(cin,plaintext);
cout<<"Enter E to encrypt or D to decrypt:\n";
cin>>action;
string zKeyword;
for (int count=0; count < plaintext.length(); count++)
{
if (keyword.length() != plaintext.length())
{
if (keyword.length()<=plaintext.length())
{
keyword = keyword+keyword[count];
}
}
}
if(action == 'E')
{
for (int i=0;i<(int)keyword.length();i++)
{
keyword[i] = toupper(keyword[i]);
alpha_to_num(keyword[i]);
}
for(int j=0;j<(int)plaintext.length(); j++)
{
plaintext[j] = toupper(plaintext[j]);
alpha_to_num(plaintext[j]);
}
for(int k=0;k<(int)plaintext.length(); k++)
{
encoding (c,plaintext[k],keyword[k]);
num_to_alpha(c);
cout<< (char)c<<endl;
ofstream myfile;
myfile.open ("example.txt" , ios::out | ios::app );
myfile << (char)c;
myfile.close();
}
}
else if(action == 'D')
{
for (int i=0;i<(int)keyword.length();i++)
{
keyword[i] = toupper(keyword[i]);
alpha_to_num(keyword[i]);
}
for(int j=0; j<(int)plaintext.length(); j++)
{
plaintext[j] = toupper(plaintext[j]);
alpha_to_num(plaintext[j]);
}
for(int m=0;m<(int)plaintext.length(); m++)
{
decoding (c,plaintext[m],keyword[m]);
num_to_alpha(c);
cout<< (char)c<<endl;
ofstream myfile;
myfile.open ("example.txt" , ios::out | ios::app );
myfile << (char)c;
myfile.close();
}
}
else
cout << "INVALID ENTRY! Please enter 'e' to encrypt or 'd to decrypt" << endl;
if( remove( "value.txt" ) != 0 )
perror( "Error deleting file" );
else
puts( "File successfully deleted" );
return 0;
}
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