Plaintext + Cipher

As for using a string's length or using the constant 8, if it were me, I would use the debugger to see what is in the length. If the number 8 works yet the length does not, then I sure would want to know what the length is and why it is not the value that it should be. You could add a line that is temporary for diagnostic purposes that would write a line to the debugging log showing what the length is when it is not 8.

If a question is definitely about C++ then please ask in the C++ forum. Especially if it is about the language.

There are many questions in the C# Language forum that should not be; they should be put in one of the other forums that are appropriate for the question. If a question is about use of .Net but the language is C++, then it is not definite where it should be. So try to do what you should do and I hope everyone will have respect and appreciation for your efforts. In otehr forusm, there would be separate forums for C++ and for other topics that are not about the language but is about programs written in C++. The CodeGuru.com forums is an example of that. Since the C# Corner web site (this one) gets so few C++ questions, it is reasonable for C++ questions to be put in the C++ forum. If however the question is much more a question of Security & Cryptography using .Net then it seems appropriate to put the question here. Hopefully you will get good at converting code between C++ and C#.

As for the difference between:

and

I don't even know where to look for Java language documentation.

If the length method of the Java String class does not always return 8 for the data and if exactly 8 bytes needs to be processed in that situation, then of course there is a difference.

In C, the string length (strlen) is determined by the first character with the value zero. The C++ std::string class determines the length in a more meaningful manner. If the code is supposed to process exactly 8 bytes and the code that uses the length property does not work then I certainly would investigate what determines the length.

And as I have said, the terminology can be confusing. In Microsoft Visual C++ there is something called MFC for doing Windows programming using C++. The MFC documentation often says that a parameter cannot be modified, but that is confusing, since it is only the address that cannot be modified; the object at that address can be modified. They could have used more precise terminology but they do not.

Your description of Java sounds similar to MFC. It would help for people learning Java to understand that. I will try to remember it.

One of the things I've always disliked about Java is that arguments are always passed by value (in the sense used by C#).

This means that you can't write a method to swap basic types unless you wrap them in a reference type first.

When you pass a reference type (i.e. a reference to an object) by value, then its the reference that gets copied. Consequently, the method does have access to the original object and so can alter its state.

I will give you my answer that I was going to give before Vulpes's so in other words this is independent of what he said.

It depends on the language. The simplified answer is that a call by reference passes an object so that it can be modified; in other words, a reference to the object is passed so the actual object can be accessed. A call by value passes the value; in other words, a copy of the data so that the data in the calling function is not modified.

The terms are meaningful in a language such as VB 6 and I assume for VB .Net too.

The terms are so confusing for the C language that I think it is foolish to use the terms for C. I would have said that regardless of what Vulpes said. In C, an address can be passed and therefore it is confusing whether that is a call by reference or a call by value. Certainly we dcan try to define what is what, but I think it is best to not even try for C.

In C++ there is the reference operator and such; I am not sure of the terminology. In C++ a reference is a new syntax for pointers, but they are usually not described as pointers and C++ references are much safer than pointers. A reference in C++ is confusing because they are used everywhere in a program, not just for function calls. Similarly, C# defines all classes as a reference type and C# has the "ref" keyword. All that is still confusing a bit for me; I suppose that ref in a function prototype is needed only for value types but all that is one thing that can be very confusing for those of us learning C#.

So my advice is to not use the terms "by reference" and "by value" for C, C++ and C# unless you are describing use of the "ref" keyword in C#. I am not sure about Java except that I assume the terms are equally confusing/meaningless for Java too.

When the terms are used, the important distinction is that by value means that the called function cannot change the data that the calling function has but by reference means that it can.

In answer to the question of "if you know about C sharp then you be able to do Java and C too?", the C++ language includes the C++ standard library and that is very different from C#. I am not familiar enough with Java enough to know if its libraries are more like C++ or C# or if they are also quite different from the others.

So eventhough the syntax of all three languages are nearly identical, there are substantial differences in the libraries. C# uses .Net (technically it is CLI) and the other two do not.

Also note that C has a runtime library that is part of the language and the C++ standard library does many of the things that the C runtime does, but not everything. So at that level, C and C++ vary in the manner that if you use C++ you tend to do things the C++ way that cannot be done using C.

For most things, the difference in performance that can be acheived by all three is usually not considered to be significant and the portability of C# and Java usually is a significant consideration. When performance is critical and portability is not a concern, C++ is considered a better choice than C# and Java.

Yes, you need to place the code (except the declarations) in a loop.

I've used a do/while loop below:

Yes you were right, my mistake - Thanks very much :)

If I want to say: Ask the user to try again without exit immediately? How can I do that? Do I have to do another loops?

I mean once user placing all the matrix; it will print "Do you want to try again" Press "Y" or "N" will Exit the console.

Then if user press "Y" it will go repeat all over again. No will exit.

Hi Vulpes,
Yes sorry I should have start new tread but...:)
Thanks for the input - I have tried them but it didnt seem give me the output I expected? Or perhaps I typed an incorrect row or columns?

As i tried this:
e.g
(1 2 3) (5)
(4 5 6) (6)
          (7)

Which the correct answer will be
(35)
(92)

Edited: Sorry I think I placed a wrong rows and columns - Thanks again yes and work great! Thanks!

You should really have started a new thread for this question (in the Visual C++ category) as it's a totally different question to the one asked originally on this thread.

However, in view of the problems we've had 'losing' threads, I'm prepared to answer it on here :)

As arrays in C++ need to be fixed size at compile time, the only thing you can do is to define the dimensions of the array to be big enough to accommodate the maximum matrix and vector sizes the user is likely to want to use. If that's 10 by 10 say, then I'd define MAX_SIZE to be 10.

The following program should do what you want:

I wonder if you could give me some assist about this program: I have implement a short program in C++ to multiply a vector by a matix
e.g
(1 2 3) (5)
(4 5 6) (6)
           (7)

Which the correct answer will be
(35)
(92)

The program need so that it is easy to change the size of the matrix and vector.

Here what I have done so far but it isn't working as I want. I wonder if would be easy to use const declaraions to specify the dimensions, any idea?

#include "stdafx.h"
#include
#include
using namespace std;
int main()
{

int **mat1;
int **mat2;
int **result;
int row,col;

cout<<"Please enter row/col"<cin>>row>>col;

mat1 = new int *[row];
mat2 = new int *[row];
result = new int *[row];
int k,i,j;

for (k=0; k  mat1[k] = new int[col];
  mat2[k] = new int[col];
  result[k] = new int[col];
 
  for (i=0; i  for (j=0; j  mat1[k][i] = k + i;
  for (j=0; j  mat2[i][k] = j + k;
  for(i=0; i  result[i][k] += (mat1 [i][k] * mat2[k][j]);

cout<}

PS: if you have a better way and simple way to demo this would be helpful. Thanks.

Limiting the string length to 8 bytes actually makes some sense, as DES has a block size of 64 bits.

Having said that the first thing I did was to test the algorithm on plaintext which was 24 bytes long and it double encrypted and decrypted fine.

But, no matter, if it's working go with it :)

Thanks Vuples, that's very helpful! Can I ask one question between C sharp an C++, I assume these two almost the same? 

OK, annotated code as follows:

Hi Vulpes,

Back to the Java code, do you mind explaining to me few lines of the code what they are actually doing so I can follow them up and maybe tweak them please.

Here the snippets of the code: