Extended Caesar Cipher C++

Question

I am trying to make and extended version of Caesar Cipher including all the 7 bit ASCII characters that's for ASCII values 32 (which is a space) to 126 (which is a tilde), but the problem is how can I make sure that my program uses only those ASCII characters and not jump into using the weird DEL symbol or the extended ASCII chart.

For ex - if I type the lowercase "u" and input 10 as for the key I will get del symbol, but I want to get a space when I type lowercase "u"

This is the code I have so far

#include <iostream>
#include <string>
#include <algorithm>
#include <iomanip>

using namespace std;

string Encrypt(string, int);

int main(int argc, char *argv[])
{
    string Source;
    int Key;

    cout << "Source: ";
    getline(cin, Source);

    cout << "Key: ";
    cin >> Key;

    cout << "Encrypted: " << Encrypt(Source, Key) << endl;
    system("pause");
}

string Encrypt(string Source, int Key)
{
    string Crypted = Source;

    for (int Current = 0; Current < Source.length(); Current++)
        Crypted[Current] += Key;

    return Crypted;
}

Answer 1

Simple: Just copy any input values outside the blessed range without modification, you just need two comparisons:

if(x<' ' || x>126)
    copy();
else
    encode();

The algorithm for caesar cipher is:

1. Map all valid symbols to consecutive non-negative numbers starting with 0
2. add the key modulo the symbol count
3. map back.

Aside: You might have to map the key before application too.

Answer 2

ok i found it what i did was just modify the formula to force the program to loop through ASCII values 32 - 126,

Crypted[Current] = ((Crypted[Current] + key) - 32) % 95 + 32;(Encrypting)
Crypted[Current] = ((Crypted[Current] - key) - 32 + 3 * 95) % 95 + 32; (Decrypting)

thanks Greg for the idea

this is the complete code working prefectly

#include <iostream>
#include <string>
#include <algorithm>
#include <iomanip>
#include <cmath>

using namespace std;

string encrypt(string, int);
string decrypt(string source, int key);
int main(int argc, char *argv[])
{
    string Source;
    int Key;

    cout << "Source: ";
    getline(cin, Source);

    cout << "Key: ";
    cin >> Key;

    cout << "Encrypted: " << decrypt(Source, Key) << endl;
    system("pause");
}

string encrypt(string source, int key)
{
    string Crypted = source;

    for (int Current = 0; Current < source.length(); Current++)
        Crypted[Current] = ((Crypted[Current] + key) - 32) % 95 + 32;
        return Crypted;
}

string decrypt(string source, int key)
{
    string Crypted = source;

    for (int Current = 0; Current < source.length(); Current++)
        Crypted[Current] = ((Crypted[Current] - key) - 32 + 3 * 95) % 95 + 32;
    return Crypted;
}