How do I peform this to an array?

I have an array of characters, for example:

"I am zack"

And want to substitute a th ("th") in place of every "z" in the array. Then I would have to store the result into another array.

Does anyone know of a way to do this? (I am just starting out)...

Thank you.

One way would be

Code:

---


        char *p = "This is zack";
        char *result = (char *)malloc(sizeof(char) * strlen(p) * 2); //multiplying by 2 because the worst case scenario would be a string in wich all characters are z

        int index = 0;
        int occurances = 0;

        for(; p[index] != '\0'; index++)
        {
                if(p[index] == 'z')
                {
                        result[index + occurances] = 't';
                        result[index + occurances + 1] = 'h';
                        occurances++;
                }
                else
                {
                        result[index + occurances] = p[index];
                }
        }


        result[index+1] = '\0';

---

@ force of will
since this is in C++, it would be best to use C++ code. that is, using c++ string objects and c++-style dynamic memory.

and more importantly, its best not to give them the solution.

The best way I have found to learn coding is by looking at codes and figuring out what they do, I just don't have all the synthax in mind to perform some algorithms, so I appreciate the suggestion.

However, i don't get some the first few lines of code(malloc...?). Yes, this is c++.

Also, I forgot to say the user is imputing(cin) the string, so strlen wouldn't really work.

I do have a way to get the length of the char array the user inputs by converting the array of a certain size (say 256) into a string and then getting the string's length.

So, at this point, I have the length of string "whatever user inputs".

with this information, can anyone provide any furthe advice?

Since the suggested solution contains at least one bug, you're probably better off not paying too much attention to it.

> Also, I forgot to say the user is imputing(cin) the string, so strlen wouldn't really work.
strlen has nothing to do with input, and strlen will work just fine on strings you input.
But since you mentioned C++, there are alternatives.

> with this information, can anyone provide any furthe advice?
Bugs aside, the posted "solution" is in the right spirit, try using the same approach yourself.

Quote:

---

Originally Posted by nadroj

@ force of will
since this is in C++, it would be best to use C++ code. that is, using c++ string objects and c++-style dynamic memory.

and more importantly, its best not to give them the solution.

---

you're totally right, i was also in the C forums and was 2:00 AM my bad.
Didint use string objects because the Fredir told he was using an array of characters

Quote:

---

Originally Posted by Salem

Since the suggested solution contains at least one bug, you're probably better off not paying too much attention to it.

---

Tell me the bug (I'm also always learning so i would appreciate it :P )

Maybe this line:

Code:

---

result[index+1] = '\0';

---

But I'm not sure - I only spent like 30 seconds looking for a potential bug.

--
Mats

yap it should be

Code:

---

result[index+ occurances] = '\0';

---

You forgot to count the \0 in your malloc call.

This is C++, so you should really use new rather than malloc.

This is C++, so you should really use std::string rather than a char array/pointer.

The low-level algorithm is:

Code:

---

For every character
  if it is a 'z'
    then write "th" to the target
    else write the character to the target

---

How you want to implement it depends on your knowledge and your intention. Do you want to learn iteration? Do you want to learn about C++'s algorithms?

I'd implement it with std::transform(), Boost.Lambda and a std::back_inserter. But that's just me.

Edit: on second thought, I probably wouldn't do it that way.

Thank you for the input everyone!

force of will, would you mind explaining what that last line is doing? I tried going one step at a time, but don't get its purpose.

Thank you once agian.

Ok, here is the code I have right now and it is not working. I would appreciate if anyone can let me know what is wrong with it:

Code:

---


#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;

#define MAX_SIZE 200



int main()
{

        int index = 0;
        int times = 0;

        char line[MAX_SIZE];

        cin.getline(line, 200);
        cout << "You entered: " << line << endl;
        string str(line);
        cout << "The size of the line is " << str.size() << " characters.\n";


        char result [256];

        for (int i=0; i < str.size(); i++)
        {
                if (line [i] == 's')
                {
                        result[i] = 'z';
                }
               
            else if (line[i] == 'r')
                {
                        result[i + times] = 'r';
                        result[i + times + 1] = 'r';
                        times ++;
                }
                else
                {
                        result[i + times] = line[i];
                }

        }
        cout << result << endl;

//        char* dest = new char[newSize + 1];




        return 0;
}

---

You need to be more specific than "it's not working".

I think you're having problems because you don't NULL-terminate your result array. Put this just before you print result:

Code:

---

result[i + times] = 0;

---

Code:

---

                if (line [i] == 's')
                {
                        result[i] = 'z';
                }
                if (line[i] == 'r')
                {
                        result[i + times] = 'r';
                        result[i + times + 1] = 'r';
                        times ++;
                }

                else
                {
                        result[i + times] = line[i];
                }

---

That second if has to be an else-if; otherwise, when line[i]=='s', the first if statement as well as the else clause will bother be executed.

You don't have to create an std::string out of your string just to determine how many characters are in the string. strlen() works just fine on char[] strings.

Code:

---

cin.getline(line, 200);

---

Why not use MAX_SIZE?

Code:

---

cin.getline(line, MAX_SIZE);

---

I'm pretty sure part of the problem is that you are not setting the end to zero, which leads to printing of "garbage" after the actual string.

If there is any other problems, please tell us what the symptoms are.

--
Mats

I am changing s into z and r into rr.

The code compiles but couts weird symbols.

That's a sure sign of a string without a NULL terminator. Add one in, see what happens.

I see...
exactly where should I include

Code:

---

result[i + times] = 0;

---

I tried putting into the loop, but it was causing the conversion part not to work at all.

If i put it outside, it just says i is not identified.

Aside from the several points that dwks pointed out, this will not work right:

Code:

---

                if (line [i] == 's')
                {
                        result[i] = 'z';
                }

---

Where are you writing the z? Is that REALLY where you want to write it, assuming your input is "resolved result"? Step through it manually and see what happens [or with a debugger if you know how to use one].

--
Mats

Quote:

---

Originally Posted by Fredir

I see...
exactly where should I include

Code:

---

result[i + times] = 0;

---

I tried putting into the loop, but it was causing the conversion part not to work at all.

If i put it outside, it just says i is not identified.

---

Move the "int i" to outside the for-loop and it will work better.

--
Mats

Code:

---

                if (line [i] == 's')
                {
                        result[i + times] = 'z';
                }
                else if (line[i] == 'r')
                {
              ...

---

These are one thing. You'll also need to null-terminate the result and make sure it is as large as needed.

Of cource, everything would be easier if you used C++ strings all the way:

Code:

---

#include <iostream>
#include <string>

int main()
{
    std::string source;
    std::getline(std::cin, source);
    std::string dest;
    for (std::size_t i = 0; i != source.size(); ++i) {
        switch (source[i]) {
            case 's': dest += 'z'; break;
            case 'r': dest += "rr"; break;
            default: dest += source[i];
        }
    }
    std::cout << source << '\n' << dest << '\n';
}

---

Oh the light!

You all have been extremely helpful, thanks for all those inputs.

I did what you suggested, and it seems to be working.

here is the updated version:

Code:

---

// C-String Lab.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;

#define MAX_SIZE 200



int main()
{

        int index = 0;
        int times = 0;

        char line[MAX_SIZE];

        cin.getline(line, 200);
        cout << "You entered: " << line << endl;
        string str(line);
        cout << "The size of the line is " << str.size() << " characters.\n";


        char result [256];
        int i;
        for (i=0; i < str.size(); i++)
        {
                if (line [i] == 's')
                {
                        result[i + times] = 'z';
                }
               
            else if (line[i] == 'r')
                {
                        result[i + times] = 'r';
                        result[i + times + 1] = 'r';
                        times ++;
                }
                else
                {
                        result[i + times] = line[i];
                }
       
               
        }
        result[i + times] = 0;
        cout << result << endl;

//        char* dest = new char[newSize + 1];




        return 0;
}

---

the next thing I have to do is to replace every "th" in the string with a "z". Would I be able to do this just by include another if stamement or should I create another for loop with result since I will be shifting indexes again?

One final question:

for the array result,

I tried making it

char result [str. length() * 2] so it would be dynamically allocated. But i got an error saying size of result cannot be 0. I am assuming this is happening because I only get an actual length once the user inputs it. But, how could I accomplish something of that effect?

You could do it in that loop. It wouldn't be too difficult. Something like this:

Code:

---

if(array[index] == 't' && array[index+1] == 'h') {
    result[rindex] = 'z';
}

---

Also note what I said above about not needing to create an entirely new std::string. You could do this instead:

Code:

---

        int i, len = strlen(line);
        for (i=0; i < len; i++)

---

You'd have to include <cstring>, which is where strlen() is located. And you could drop <string>, as yuo wouldn't be using any std::strings.

[edit]

Quote:

---

I tried making it

char result [str. length() * 2] so it would be dynamically allocated. But i got an error saying size of result cannot be 0. I am assuming this is happening because I only get an actual length once the user inputs it. But, how could I accomplish something of that effect?

---

I don't think you can declare variable-sized arrays in standard C++. Try this instead:

Code:

---

char *result = new char[str.length() * 2];

// ...

delete [] result;

---

I'd use str.length()*2+1 for the size, though, because that's the maximum it could be. Don't forget the NULL. :) [/edit]

Code:

---

for (k =0; k < size of result; i++)
{
if (result[k] == 't' && result[k+1] == 'h')
 newResult[k] == 'z';
}

---

--> does this seem to be in the right track?

[EDIT] thanks dwks, I guess I had the idea...let me incorporate those things in...

I don't think the if statement is working... I will see if I can do the above loop later:

Code:

---

// C-String Lab.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;

#define MAX_SIZE 200



int main()
{

        int index = 0;
        int times = 0;

        char line[MAX_SIZE];

        cin.getline(line, 200);
        cout << "You entered: " << line << endl;
        string str(line);
        cout << "The size of the line is " << str.size() << " characters.\n";


        char result [256];
        int i;
       
        for (i=0; i < str.size(); i++)
        {
                if (line [i] == 's')
                {
                        result[i + times] = 'z';
                }
               
            else if (line[i] == 'r')
                {
                        result[i + times] = 'r';
                        result[i + times + 1] = 'r';
                        times ++;
                }
                if (result[i] == 't' && result[i+1] == 'h')
                {
                        result[i] == 'z';
                }
                else
                {
                        result[i + times] = line[i];
                }
               
               
        }
        result[i + times] = 0;
        cout << result << endl;

//        char* dest = new char[newSize + 1];




        return 0;
}

---

Code:

---

else if (line[i] == 'r')
...
if (result[i] == 't' && result[i+1] == 'h')

---

See anything different.

--
Mats

The code doesn't take unicode into mind either. It's good practice to try to use TCHAR functions and _T() macro to make it both unicode/ansi safe. It takes some getting used to, I've found out.

Ok, looks like I completed the code. Here is the final version:

Code:

---

#include "stdafx.h"
#include <iostream>
#include <cstring>

using namespace std;

#define MAX_SIZE 200



int main()
{

        int index = 0;
        int times = 0;

        char line[MAX_SIZE];

        cin.getline(line, MAX_SIZE);
        cout << "You entered: " << line << endl;
        cout << "The size of the line is " << strlen(line) << " characters.\n";

        int len = strlen(line);
        char* result = new char[len*2 +1];
        int i;

        for (i=0; i < len; i++)
        {
                if (line [i] == 's')
                {
                        result[i + times] = 'z';
                }
                else if (line[i] == 'r')
                {
                        result[i + times] = 'r';
                        result[i + times + 1] = 'r';
                        times ++;
                }
                else if (line[i] == 't' && line[i+1] == 'h')
                {
                        result[i + times] = 'z';
                }
                else
                {
                        result[i + times] = line[i];
                }


        }

        result[i + times] = 0;
        cout << "Translation: " << result << endl;
        delete [] result;


        return 0;
}

---

Thank you all for the help. If anyone wants to give tips as how to make the code more efficient for my own benefit in the future, that would be nice.

Your code is pretty good now. One of my only suggestions is this:

Code:

---

        cout << "The size of the line is " << strlen(line) << " characters.\n";

        int len = strlen(line);

---

Swap those lines, and you can use the variable len in the cout. strlen() does take a little while to execute, so your program will be marginally more efficient if you do as I suggest.

Quote:

---

Originally Posted by Elysia

The code doesn't take unicode into mind either. It's good practice to try to use TCHAR functions and _T() macro to make it both unicode/ansi safe. It takes some getting used to, I've found out.

---

Both of those are Windows-only functions. You shouldn't recommend them in a program that is otherwise perfectly standard C++. On the other hand, because the OP is including "stdafx.h", they're clearly using a Windows compiler (probably MSVC). Still, when you recommend things like that, at least mention in passing that they're Windows-specific.

Quote:

---

Originally Posted by dwks

Both of those are Windows-only functions. You shouldn't recommend them in a program that is otherwise perfectly standard C++. On the other hand, because the OP is including "stdafx.h", they're clearly using a Windows compiler (probably MSVC). Still, when you recommend things like that, at least mention in passing that they're Windows-specific.

---

Unicode Windows-specific? Last I looked, using TCHAR resolved to either CHAR or WCHAR_T and ANSI/UNICODE C/C++ standard functions (as well as Windows-only API).

TCHAR is a typedef defined in windows.h, TEXT() is a macro defined in windows.h. That's certainly Windows-specific. You can emulate them on other platforms, of course.

The _TCHAR typedef and the _T() and _TEXT() macros are defined in tchar.h, which is a Microsoft-specific header, although other Windows vendors probably provide it too, for compatibility.

The whole point of the duality there is that Win9x and below use narrow characters natively, while WinNT uses UTF-16 natively and narrow characters only in emulation, which imposes a speed penalty. Furthermore, WinCE and derivates do not support the narrow APIs at all. Therefore, in the interest of Win32 code reuse, it's a good idea to use the UNICODE switch to make your code compatible with both modes.

In non-Win32, portable programs, the same thing is a huge waste of effort. Other than Win32, I know of no system API or cross-platform library that provides both narrow and wide character interfaces. Therefore, in order to support both, you would have to write your own wrappers.

The whole point of using _T is to make your program able to compile with both UNICODE and ANSI without any code changes, as the situation requires it.

Please don't get me started on character encodings in C++.

Ah, whatever...