Need help encoding C++ strings by increasing ASCII value - c++

Question

I've looked around everywhere for a C++ code that takes a message from the user, and encodes it by increasing the ASCII value of each character (obviously not very secure, but simple enough). I've managed to put together a program that returns a character of a few values higher, but can not figure out how to do it with a full message including spaces. I plan to make a decoder that does the opposite afterwards. Any help would be really appreciated. Thanks in advance.
Single Value C++ Program -
#include <iostream>
using namespace std;
int main(){
char ascii;
cout << "Enter a character: ";
cin >> ascii;
cout << "Its ascii value is: " << (int) ascii << endl;
return 0;
}
Working Encoder Example in VBS -
set x = WScript.CreateObject("WScript.Shell")
entxtde = inputbox("Enter text to be encoded")
entxtde = StrReverse(entxtde)
x.Run "%windir%\notepad"
wscript.sleep 1000
x.sendkeys encode(entxtde)
function encode(s)
For i = 1 To Len(s)
newtxt = Mid(s, i, 1)
newtxt = Chr(Asc(newtxt)+3)
coded = coded & newtxt
Next
encode = coded
End Function

Answer 1

std::string originalString = "";
std::string newString = "";
int incrementValue = 1;
std::cout << "Input a string to encode: ";
std::cin >> originalString;
for(int i = 0; i < originalString.length(); i++) {
newString += (originalString.at(i) + incrementValue);
}
std::cout >> "New string is " + newString
Just change incrementValue to change how it's encoded.
"Hello" = "Ifmmp" if incrementValue = 1
To reverse it, just change it to subtract incrementValue instead of add in the same kind of for loop. Simple enough I think

Answer 2

This may be done in a single line, or two if you want to stay under 80 columns. Where value is the string you wish to encrypt, and offset the offset value:
auto caesar = [offset](CharT c){return c + offset;};
std::transform(value.begin(), value.end(), value.begin(), caesar);
For bonus points you can make it work with any kind of string by templating on character type:
template <typename CharT>
std::basic_string<CharT> caesarEncode(std::basic_string<CharT> value, CharT offset){
auto caesar = [offset](CharT c){return c + offset;};
std::transform(value.begin(), value.end(), value.begin(), caesar);
return value;
}
Since it looks like you may be experiencing difficulties actually obtaining a string with whitespace, you may get one using the getline function of the standard library, which by default obtains one full line of the source stream.
// narrow (CharT = char)
std::string value;
std::getline(std::cin, value);
// wide (CharT = wchar_t)
std::wstring wvalue;
std::getline(std::wcin, wvalue);
for which actually encoding the string would be done as follows:
char offset = 12;
auto encoded = caesarEncode(value, offset);
wchar_t woffset = 12;
auto wencoded = caesarEncode(wvalue, woffset);
You can see an example in practice here on coliru.

Answer 3

It's simple really. First you take your input as a string. Then, iterate through each character adding by what you want. To ensure the value remains valid and easy to reverse, you mod that value by the max value of a char, i.e. 255.
int main () {
std::string input; // to store the text
std::getline(std::cin, input); // get the text
const int _add = 12; // value added
const int max_size = 255; // max value of a char
for (int i = 0; i < input.size(); ++i)
input[i] = (input[i] + _add) % max_size;
/* now the input is properly modified */
}
note: _add is an int to prevent overflow errors.