String proplem!!!!Please help

Write the following member function:
// strcmp is negative if s < s1
// is 0 if s == s1
// and positive if s > s1
// where s is the emplicite argument

int my_string::strcmp(const my_string& s1);


// strrev reverses the my_string
void my_string::strrev();


//print oeverloaded to print the frist n characters
void my_string:: print(int n);


here is what i got so far:

Code:

---

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


using namespace std;

class my_string
{
public:
  my_string();
  my_string(const my_string& str);
  my_string(const char* p);
  ~my_string();

  int strcmp(const my_string& s1);
  void strrev();
  void print(int n);

  int const getLen();
  const char* getS();
private:
      char* s;
      int len;
};


my_string::my_string(): len(0),s (0){}

my_string::my_string(const char* p)
{
  len = strlen (p);
  s = new char[len +1];
  assert(s !=0);
  strcpy(s, p);
}


my_string::my_string(const my_string& str):len(str.len)
{
  s = new char[len+1];
  assert(s !=0);
  strcpy(s, str.s);
}


// Destructor
my_string::~my_string()
{
  delete [] s;
}


int my_string::strcmp(const my_string& s1)
{
  int i;
  for(i=0; s1.s[i] && s[i] && s1.s[i] == s[i]; ++i)
  {

      return s1.s[i]-s[i];
  }
}


void my_string::strrev()
{
    my_string strrev;
    char* temp = new char[len + 1];
    int i= 0;
    int j= 0;
    while (s[i])
    {
      temp[j++] = s[i--];
    }
    temp[j] ='\0';
    strcpy(s,temp);
    delete[] temp;
}


void my_string:: print(int n)
{

  return ;
}


int const my_string::getLen()
{
  return len;
}


const char* my_string::getS()
{
  return s;
}


int main ()
{

  my_string myStr ("same");

  if (myStr.strcmp ("same") < 0)
      cout << myStr.getS() << " < " << "same" << endl;
  else if (myStr.strcmp ("same") == 0)
      cout << myStr.getS() << " = " << "same" << endl;
  else
      cout << myStr.getS() << " > " << "same" << endl;
  cout << "Reverse string " << myStr.getS() << " to ";
  myStr.strrev();
  myStr.print();
  system("pause");
}

---

when i compile it ,the compiler telling me the error: " No matching function for call to my_string:: print()" and "Candidates are : void my_string:: print()".Please tell me where did i go wrong,thanks alot

Note:

Code:

---

Use the following string to test the function strcmp:
      1st string                                2nd string
      gladiator                                gladiolus
      xyz                                          abcd
      same                                      same

---

Are you allowed to have a space in this: void my_string:: print(int n)

Shouldn't it be: void my_string::print(int n)

??

Quote:

---

Originally posted by kasracer
Are you allowed to have a space in this: void my_string:: print(int n)

Shouldn't it be: void my_string::print(int n)

??

---

yea,you are right,the reason i did that because the forum can't recognize ::p instead of :: p when i'm using .You can try and see how funny with vbb forums

... and where is my_string::print () , without any arguments, declared??

Check to see if you can use the return statement in a void function like you've done below:

Code:

---

void my_string::print(int n)
{

  return ;
}

---

Then, I don't think you can call print without passing any parameter:

Code:

---

myStr.print();

---

What do you get?

Quote:

---

Originally posted by tinhnho
when i compile it ,the compiler telling me the error: " No matching function for call to my_string:: print()" and "Candidates are : void my_string:: print()".Please tell me where did i go wrong,thanks alot

---

First, when posting, note that you have a "Disable Smilies in this post" option below the edit window.

Second, the reason for the error is obvious: your print() member function takes an integer argument, but you called it without an argument.

Third, your class has no assignment operator. If I did this, your code would not be correct:

Code:

---

int main()
{
  my_string s = "ABC";
  my_string t;
  t = s;
}

---

You will now have two objects pointing to the same dynamically allocated char *. On destruction, you will delete the same memory twice.

Regards,

Paul McKenzie

you might think about adding an assigment operator.. like paul suggested. It makes your class a lot more useful and predictable.
But your code as written doesn't requre this.

here is your fix with explainations

Code:

---

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



using namespace std;

class my_string
{
public:
  my_string();
  my_string(const my_string& str);
  my_string(const char* p);
  ~my_string();

  int strcmp(const my_string& s1);
  void strrev();
  void print(int n = -1);            // added the parameter defaut so you can use without
                                // any parameters like you are doing

  int const getLen();
  const char* getS();
private:
      char* s;
      int len;
};


my_string::my_string(): len(0),s(0) {}   

my_string::my_string(const char* p)
{
  len = strlen (p);
  s = new char[len +1];
  assert(s != 0);     

  strcpy(s, p);
}


my_string::my_string(const my_string& str):len(str.len)
{
  s = new char[len+1];
  assert(s !=0);

  strcpy(s, str.s);
}


// Destructor
my_string::~my_string()
{
  delete [] s;
}


int my_string::strcmp(const my_string& s1)
{
  int iMinLen = 0;

  iMinLen = (len < s1.len) ? len : s1.len;

// int i;
// for(i=0; s1.s[i] && s[i] && s1.s[i] == s[i]; ++i)          // JMS old line
  for( int i = 0; i < iMinLen; i++ )
  {
          if ( s[i] > s1.s[i] )  // JMS need to do this char by char...
          {
                  return 1;                          // JMS s > s1
          }
          else
          {
                if ( s[i] < s1.s[i] )  // JMS need to do this char by char...
                {
                        return -1;        // JMS s < s1
                }
          }

          // else both chars are equal so move on to the next char

//      return s1.s[i]-s[i];    // JMS removed
  }

  // Now both strings are equal up to the minimum length of eather string...

  // if the strings are the same size then they are equal
  if ( s1.len == len )
          return 0;

  // s1 ="123"  s = "12"  s is less than
  if ( s1.len > len )
  {
          return -1;
  }
  else
  {  // s is greater..
          return 1;
  }
}


void my_string::strrev()
{
//    my_string strrev;                    // JMS removed your not using it
    char* temp = new char[len + 1];
        memset( temp, '\0', len+1);            //        set the entire string to '\0'
//  int i= 0;

    int j= len-1;  // 'same' len == 4.... 0-3(j) == 4... get it...


//  while (s[i])

        for ( int i = 0; i < len; i++ )
    {
      temp[i] = s[j];
          j -= 1;
    }
//  temp[len] ='\0';
    strcpy(s,temp);
    delete[] temp;
}


void my_string:: print(int n)
{
        if ( n == -1 )
        {
                printf("%s", s );
        }
        else
        {
                char* temp = new char[n + 1];
                memset( temp, '\0', len+1);            //        set the entire string to '\0'

                strncpy( temp, s, n );
                printf("%s", temp );
                delete []temp;
        }

  return ;
}


int const my_string::getLen()
{
  return len;
}


const char* my_string::getS()
{
  return s;
}


int main(int argc, char* argv[])          // JMS  changed main parameters cause I neeeeeded too..
{

        // this code added to make it simpler to swap around values..
        char szString1[10] = "same";        // use same
        char szString2[10] = "ralphie";        // use same(same = same) same1(same < same1) sam(same > sam) ralphie(same>ralphie)


        // (same>ralphie)  I guess this is ok because "at" appears in the dictionary before zoo even if
        // 77 is smaller than 666...


  my_string myStr (szString1);

  if (myStr.strcmp (szString2) < 0)
      cout << myStr.getS() << " < " << szString2 << endl;
  else if (myStr.strcmp (szString2) == 0)
      cout << myStr.getS() << " = " << szString2 << endl;
  else
      cout << myStr.getS() << " > " << szString2 << endl;
  cout << "Reverse string " << myStr.getS() << " to ";
  myStr.strrev();
  myStr.print();
  cout << endl;                              // jms added

  system("pause");

  return 0;                       
}

---

Well...just out of curiosity...why do you need to build your own string class?

here is what i have done.I compiled it and it said something about run time error , there are no message error.I'm using Dev C++.Thanks

Code:

---

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

using std::cout;

class my_string
{
public:
  my_string();
  my_string(const my_string& str);
  my_string(const char* p);
  ~my_string();

  int strcmp(const my_string& s1);
  void strrev();
  void print(int n=0);
  int const getLen();
  const char* getS();
private:
  char* s;
  int len;
};


my_string::my_string(): len(0),s (0){}

my_string::my_string(const char* p)
{
  len = strlen (p);
  s = new char[len +1];
  assert(s !=0);
  strcpy(s, p);
}


my_string::my_string(const my_string& str):len(str.len)
{
  s = new char[len+1];
  assert(s !=0);
  strcpy(s, str.s);
}


// Destructor
my_string::~my_string()
{
  delete [] s;
}


//strcmp
int my_string::strcmp(const my_string& s1)
{
  int i;
  while(s1.s[i] && s[i] && s1.s[i] == s[i])
  {
      i++;
  }
  return s1.s[i]-s[i];
}



//strrev
void my_string::strrev()
{
  char* temp = new char[len + 1];
  int i = len -1;
  int j= 0;
  while (s[i])
  {
      temp[j++] = s[i--];
  }
  temp[j] ='\0';
  strcpy(s,temp);
  delete[] temp;
}


void my_string::print(int n)
{
  if (n > len || n == 0) n = len;
  for (int i = 0; i < n; ++i)
  cout << s[i];
  cout << endl;
}



int const my_string::getLen()
{
  return len;
}


const char* my_string::getS()
{
  return s;
}


int main ()
{
  my_string myStr("gladiator");
  if (myStr.strcmp ("gladiolus") < 0)
      cout << myStr.getS() << " < " << "gladiolus" << endl;
  else if (myStr.strcmp ("gladiolus") == 0)
      cout << myStr.getS() << " = " << "gladiolus" << endl;
  else
      cout << myStr.getS() << " > " << "gladiolus" << endl;
  cout << "Reverse string " << myStr.getS() << " to ";
  myStr.strrev();
  myStr.print();
  system("pause");
}

---

Are you using a debugger? If not, please do so, since the problem is easily found. Dev-C++ has a debugger.

Code:

---

int my_string::strcmp(const my_string& s1)
{
  int i;
  while(s1.s[i] && s[i] && s1.s[i] == s[i])

---

The value of "i" is uninitialized. It could be anything. Initialize it to 0.

Regards,

Paul McKenzie

Quote:

---

Originally posted by Paul McKenzie
The value of "i" is uninitialized. It could be anything. Initialize it to 0.

---

Even though I do agree with you, I thought MinGW and MS C++ compilers both initialized integers to 0 automatically when it isn't specified. Or is that only in the global scope? Or am I just totally off?

Quote:

---

Originally posted by Paul McKenzie
Are you using a debugger? If not, please do so, since the problem is easily found. Dev-C++ has a debugger.

Code:

---

int my_string::strcmp(const my_string& s1)
{
  int i;
  while(s1.s[i] && s[i] && s1.s[i] == s[i])

---

The value of "i" is uninitialized. It could be anything. Initialize it to 0.

Regards,

Paul McKenzie

---

no, i am not.and i dont know how to use debugger!!!.Since my instructor only teach us write the program but never teach us how to debug the program!!!...poor us..Anyone know how to debug ?and now any totorial which helpfull for Dev C++ ?My school is really suck they have all software which are VC++ pro edition... but they're teaching us with Dev C++ which free complier!!!? ... :( what the poor guys!!!..Last word,anyone try to compiles and tell me where the error is,and debug if you can..Thanks..

note: I compiled it and it still saying that error which about run time error...and try to jump to debugger...=>since i dont know how to debug.Sorry bother everyone,but i just wanna learn new thing and want some one correct me...Thanks for reading

Quote:

---

Originally posted by kasracer
Even though I do agree with you, I thought MinGW and MS C++ compilers both initialized integers to 0 automatically when it isn't specified. Or is that only in the global scope? Or am I just totally off?

---

In C++, local variables are not automatically initialized. You cannot assume what a compiler may or may not do -- automatic (local) variables are uninitialized when declared. In any event, I ran the code in release mode of VC++, and the "i" is not initialized.

Regards,

Paul McKenzie

Quote:

---

Originally posted by tinhnho
no, i am not.and i dont know how to use debugger!!!.Since my instructor only teach us write the program but never teach us how to debug the program!!!...

---

how about learning yourself.

/Seems to big the biggest problem with college goers.

Quote:

---

Originally posted by tinhnho
no, i am not.and i dont know how to use debugger!!!.Since my instructor only teach us write the program but never teach us how to debug the program!!!

---

You don't need a teacher -- the Dev-C++ IDE has a "Debug" menu. Why not try it for yourself and see how it works? Sometimes you have to go one step beyond what you are being taught.

Anyway, tell your teacher that the string class you are writing lacks an assignment operator. I'm surprised that a teacher of C++ wouldn't have taken note of this.

Quote:

---

but they're teaching us with Dev C++ which free complier!!!?

---

Dev C++ is based on the gcc compiler, and gcc is one of the best out there in terms of C++ compliance. So in many ways, Dev-C++ utilizes a better compiler (gcc) than Visual C++ (version 6.0).

Quote:

---

I compiled it and it still saying that error which about run time error...and try to jump to debugger...=>since i dont know how to debug.

---

First, you are getting an error when you are running the program, not when you're compiling it. Hopefully the teacher has explained the difference between a compiler error and a run-time error.

Second, all you need to debug your program is to go to the Debug menu after you have compiled your program. You just don't execute your program, which is what I believe you are doing now. It isn't very difficult, just go to the Debug menu and select "Debug" instead of executing your program. All the other options in the Debug menu are either self-explanatory, or will be explained to you if you take the time and experiment with it.

Regards,

Paul McKenzie