Ceaser Cipher encryption

[mamq3]

Hi all!

I am having an issue with one of my assignment of Cypher decrypting. I wanted to create a cypher class. This class will have a constructor which takes a 2 parameter key, and applies an affine shift of the form f(x) = ax + b, where the output character is the cyphertext of the plaintext character x.
javascript:PostPreview()
I am getting several errors.

Following is my code:

#include<iostream>
#include<cstdlib>

using namespace std;

class Cypher

{
public:
	Cypher(int aVal, int bVal);

	Cypher();

	void setMessage(char Message[20]);
	void getMessage();
private:

	int a;
	int b;
	char decrypted[20];

};


int main()
{
	Cypher cypher1(3, 4);

	cout << "Decrypted message: \n";
	cypher1.setMessage("abcd");
	cout << cypher1.getMessage() << endl;
}

Cypher::Cypher(int aVal, int bVal) : a(aVal), b(bVal)
{
}

Cypher::Cypher() : a(1), b(1)
{
}

void Cypher::setMessage(char Message[20])
{
	int i = 0;
	while (Message[i] != "\0")){

	Message[i] = char((a*Message[i] + b)%26 + 65);
	}
	decrypted = Message;
}

void Cypher::getMessage()
{
	return decrypted;
}

I would really appreciate any of your help.

[Smac89]

Welcome to cplusplus!

The nature of the error you are receiving is not known to us. It would help if you:

1. Put your code in code tags ("<>")
2. State what line is producing the error in your code
3. Paste the errors you are recieving

[Catfish3]

and applies an affine shift of the form f(x) = ax + b

The Caesar cipher works like this:

alphabet = "abcdefghijklmnopqrstuvwxyz"

(user enters shift n == 2)
(user enters message msg == "hello")

(computing message enc from msg and n)
h -> j
e -> g
l -> n
l -> n
o -> q

(enc == "jgnnq")

I would really appreciate any of your help.

I have a suggestion: use std::string (C++ string) instead of char[20] (C string).
http://cplusplus.com/reference/string/basic_string/

[mamq3]

Thank you guys for your suggestions. I used std::string but it still showing lots of errors. some of them are showing below:

error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'void' (or there is no acceptable conversion)
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(679): could be 'std::basic_ostream<_Elem,_Traits> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<_Elem,_Traits> &,const char *)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]

I am pasting my changed code again:

#include<iostream>
#include<cstdlib>
#include<string>

using namespace std;

class Cypher

{
public:
	Cypher(int aVal, int bVal);

	Cypher();

	void setMessage(string Message);
	void getMessage();
private:

	int a;
	int b;
	string decrypted;

};


int main()
{
	Cypher cypher1(3, 4);

	cout << "Decrypted message: \n";
	cypher1.setMessage("abcd");
	cout << cypher1.getMessage() << endl;
}

Cypher::Cypher(int aVal, int bVal) : a(aVal), b(bVal)
{
}

Cypher::Cypher() : a(1), b(1)
{
}

void Cypher::setMessage(string Message)
{
	int i = 0;
	while (Message[i] != "\0")){

	Message[i] = char((a*Message[i] + b)%26 + 65);
	}
	decrypted = Message;
}

void Cypher::getMessage()
{
	return decrypted;
}

Thank you again for your help.

[Catfish3]

string Cypher::getMessage()
{
	return decrypted;
}

I do not understand why you use the combination of a and b instead of a single shift n.

Also your while() in Cypher::setMessage() can be rewritten as:

for (std::string::iterator it = Message.begin(); it != Message.end(); ++it)
    *it = char((a * (*it) + b) % 26 + 65);

or

for (size_t i=0; i < Message.length(); ++i)
    Message[i] = char((a*Message[i] + b)%26 + 65);

If you're using Visual Studio 2012 which supports C++11 (the C++ standard of 2011), you can use range-based for() loops.

for (char ch: Message)
    ch = char((a * ch + b) % 26 + 65);