Removing all white-spaces from a string

Continuing on the same theme as the last post. What if all the spaces need to be stripped out from the input string:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>
#include<string>

using namespace std;

string removeAllSpaces(const string& s)
{
 string newStr(s);
 bool spacesLeft = true;

 while(spacesLeft)
 {
   int pos = newStr.find(" ");
   if(pos != string::npos)
   {
     newStr.erase(pos, 1);
   }
   else
     spacesLeft = false;
 }

 return newStr;
}

int main()
{
 string aString("This  string   has        multiple spaces     problem!");

 cout<<"Original : "<<aString<<endl;
 cout<<"Modified : "<<removeAllSpaces(aString)<<endl;

 return 0;
}

The output is as follows:

Removing Multiple White-spaces from a string

A simple program to remove an arbitrary number of white spaces in between words. Program as follows:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>
#include<string>

using namespace std;
 
bool removeDoubleSpaces(string& s)
{
  bool found = true;
 
  int i = s.find("  "); //Search for 2 spaces
  if(i != string::npos)
  {
    s.replace(i, 2, " ");
  }
  else
    found = false;
 
  return found;
}
 
string removeMultipleSpaces(const string& s)
{
  string newStr(s);
  bool found = true;
 
  while(found)
  {
    found = removeDoubleSpaces(newStr);
  }
 
  return newStr;
}
 
int main()
{
  string aString("This  string   has        multiple spaces     problem!");
 
  cout<<"Original : "<<aString<<endl;
  cout<<"Modified : "<<removeMultipleSpaces(aString)<<endl;
 
  return 0;
}
 

The output is as follows:

A generic sort program with 'functors' and 'templates'

Picked up this question from here and made a program out of it. It may be a good idea to quickly brush functors and templates if required.

The program sorts the input Vector provided regardless of the type.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

using namespace std;

class Int
{
public:
  Int() {x_ = 0;}
  Int(const int &x) {x_ = x;}
  int getID (void) {return x_;}
  int x_;
};

class Str
{
public:
  Str() {x_ = "";}
  Str(const string &x) {x_ = x;}
  string getID (void) {return x_;}
  string x_;
};

template <typename Object> class Comparator {
  public:
    bool operator()(const Object &o1, const Object &o2) const 
    {
      return (const_cast<Object&>(o1).getID() < const_cast<Object&>(o2).getID());
    }

    bool operator()(const Object *o1, const Object *o2) const {
      return (o1->getID() < o2->getID());
    }
};

template <typename VecObject> void Display(VecObject v)
{
  VecObject::iterator it;
  for(it = v.begin(); it != v.end(); ++it)
  {
    cout<<it->getID()<<", ";
  }
  cout<<endl;
}

int main()
{
  vector<Int> objects1;
  objects1.push_back(Int(3));
  objects1.push_back(Int());
  objects1.push_back(Int(77));

  //print the output
  cout<<"objects1 before sort = ";
  Display(objects1);
  std::sort(objects1.begin(), objects1.end(), Comparator<Int> ());
  cout<<"objects1 after sort  = ";
  Display(objects1);

  std::vector<Str> objects2;
  objects2.push_back(Str("Hello Hello"));
  objects2.push_back(Str("apple?"));
  objects2.push_back(Str());
  objects2.push_back(Str("1 Jump"));

  //print the output
  cout<<"objects2 before sort = ";
  Display(objects2);
  std::sort(objects2.begin(), objects2.end(), Comparator<Str> ());
  cout<<"objects2 after sort  = ";
  Display(objects2);

  return 0;
}

The output is as follows:

Debugging Mutex and Locks

When there are multiple Mutex's in the program, it may be required to find if a particular thread is locked far longer than necessary. This can cause problems and the output may not be what is expected.

To get round this, I took an old example from here and modified it to help me print some debugging info.

I modified the printSomething() in Singleton.h to add a sleep as follows:

  void printSomething(char *name, int count)
 {
   Lock guard(mutex_);
   Sleep(10);
   Lock guard2(mutex_);
   std::cout << name << " loop " << count << std::endl;
 }

and I modified the Mutex.h as follows:

//Example from http://www.relisoft.com/Win32/active.html
#if !defined _MUTEX_H_
#define _MUTEX_H_

class Mutex
{
   friend class Lock;
public:
   Mutex () { InitializeCriticalSection (& _critSection); }
   ~Mutex () { DeleteCriticalSection (& _critSection); }
private:
   void Acquire ()
   {
     DWORD start = GetTickCount();
     EnterCriticalSection (& _critSection);
     DWORD elapsed = GetTickCount() - start;
     if (elapsed > 15)
     {
       //Debugging Info
        std::cout<<"Debugging Info: Waited at mutex for "<<elapsed<<std::endl;
     }
   }
   void Release ()
   {
       LeaveCriticalSection (& _critSection);
   }

   CRITICAL_SECTION _critSection;
};

#endif 

The output is as follows:

The small problem with the above approach is that if a Thread is deadlocked, we may not get the debug output as we would have to kill the process.

Add two unsigned integers without using '+'

I found this very interesting discussion (and the program) to add two numbers without the use of the arithmetic operator '+'. The obvious guess would be to use the Bitwise operators.

The logic behind the addition operation using the bitwise operators is as follows:

integer1 =  3  = 0011b
integer2 =  5  = 0101b

    first operation        second operation      third operation
        0011                0011                 shift by one
        0101                0101                   
       ______              ______
 XOR    0110           AND  0001  ------>        <<1   0010

    Again...  
                   first operation   second operation   third operation
previous XOR        0110                0110            shift by one
previous <<1        0010                0010
                   ______              ______
               XOR  0100            AND 0010  ------>  <<1   0100

    Again...  
                   first operation  second operation    third operation
previous XOR        0100                0100            shift by one
previous <<1        0100                0100
                   ______              ______
                XOR 0000           AND  0100  ------>  <<1   1000

    Again...  
                   first operation   second operation   
previous XOR        0000               0000            
previous <<1        1000               1000
                    ______            ______
                XOR 1000          AND  0000  
When AND iguals 0 the result of XOR is iqual to the sum of the two integers

The program is as follows:

//Program to add two numbers by using boolean operators
//Ref: http://www.daniweb.com/forums/thread84950.html
//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>

using namespace std;

unsigned long add(unsigned integer1, unsigned integer2)
{
  unsigned long xor, and, temp;

  and = integer1 & integer2; /* Obtain the carry bits */
  xor = integer1 ^ integer2; /* resulting bits */
    
  while(and != 0 ) /* stop when carry bits are gone */
  {
    and <<= 1; /* shifting the carry bits one space */
    temp = xor ^ and; /* hold the new xor result bits*/
    and &= xor; /* clear the previous carry bits and assign the new carry bits */
    xor = temp; /* resulting bits */
  }
  return xor; /* final result */
}

int main()
{
  int num1 = 13, num2 = 27;

  cout << num1 << " + " << num2 << " = " <<add(num1, num2) << endl;

  return 0;
}

The output is:

13 + 27 = 40

See the original discussion here.

Consequences of Ignoring Compiler Warnings

Though this is a fictional program that I have picked up from here, I have seen similar problems in real life.

Lets say my program (below) was expected to return this

but instead returned:

Program as follows:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>

using namespace std;

class Bclass
{
public:
 Bclass() {}
 virtual void func()
 {
   cout<<"In Bclass::func()"<<endl;
 }
};

class Dclass : public Bclass
{
public:
 Dclass() {}
 virtual void func()
 {
   cout<<"In Dclass::func()"<<endl;
   Bclass:func();
 }
};

int main()
{
 Dclass d;
 d.func();
 //...
  return 0;
}

The clue of the problem was given by the compiler that generated the following warning:

main.cpp(23) : warning C4102: 'Bclass' : unreferenced label

pointing to the line

Bclass:func();

The problem lies in the fact that due to a single : rather than :: the line above is being treated as label and since its an unreferenced label it goes back to the start of the same function.

You can read the complete discussion here. Make sure to check the warnings the next time your program behaves unexpectedly.

Swap two variables without using third and in one line

Couple of weeks back I was interviewing a fresh graduate. Even though they are taught programming, I am not sure if they take it seriously and learn or practice it well. One of the questions I asked was to swap 2 numbers without using a temp variable.

Looking back now, I think it may be a bigger challenge to ask to swap numbers without using a temp variable and in one line. Below are my three different approaches but I would advise you to try it yourself before looking at the answer.

//Program to swap 2 numbers without using 3rd variable and in one line
//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>

using namespace std;

void approach1(int& a, int& b)
{
  cout<<"\nApproach 1"<<endl;
  a^=b^=a^=b;
}

void approach2(int& a, int& b)
{
  cout<<"\nApproach 2"<<endl;
  //b=(a+b)-(a=b); - This should work but doesnt, why?
  a =((a = a + b) - (b = a - b)); 
}

void approach3(int& a, int& b)
{
  cout<<"\nApproach 3"<<endl;
  a = ((a = a * b) / (b = a / b));
}



int main()
{
  int a = 13, b = 29;
  cout<<"\nOriginal"<<endl;
  cout<<"a = "<<a<<", b = "<<b<<endl;

  approach1(a, b);
  cout<<"a = "<<a<<", b = "<<b<<endl;

  a = 13, b = 29;
  approach2(a, b);
  cout<<"a = "<<a<<", b = "<<b<<endl;

  a = 13, b = 29;
  approach3(a, b);
  cout<<"a = "<<a<<", b = "<<b<<endl;

  return 0;
}

The output is as follows:

Agreed that the above would be applicable only for integers.

'sizeof' a class

Continuation from last week. What is the sizeof of a class? Wrote a simple program as follows:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>

using namespace std;

class A
{
  int a;
};

class B
{
  int b;
  int someFunc(void) {return b;}
};

class C
{
  void someFunc1(void) {};
  void someFunc2(void) {};
};

class D : public A
{
  void someFunc(void) {};
};


int main()
{
  cout<<"Size of class A = "<<sizeof(A)<<endl;
  cout<<"Size of class B = "<<sizeof(B)<<endl;
  cout<<"Size of class C = "<<sizeof(C)<<endl;
  cout<<"Size of class D = "<<sizeof(D)<<endl;
}

The output is as follows:

After finishing this, I found this interesting article here.

Checking the 'sizeof' doubts

I noticed sometime back that one of my programs behaved unexpectedly in certain scenarios which was traced to an incorrect use of sizeof. As a result, I made a small program to make sure that my understanding of sizeof is correct. Here is the program:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>

using namespace std;

int main()
{
 char a[]="";
 cout<<"Size of a[] = "<<sizeof(a)<<endl;

 char b[]=" ";
 cout<<"Size of b[ ] = "<<sizeof(b)<<endl;

 char c[10];
 cout<<"Size of c[10] = "<<sizeof(c)<<endl;

 char* d;
 cout<<"Size of d = "<<sizeof(d)<<endl;

 char* e = c;
 cout<<"Size of e = "<<sizeof(e)<<endl;

 char f[] = "123456";
 cout<<"Size of f = "<<sizeof(f)<<endl;

 char g[] = {'1','2','3','4','5','6'};
 cout<<"Size of g = "<<sizeof(g)<<endl;

 return 0;
}

The output is as follows:

A lot of interviewers love the sizeof questions.

Have you come across any interesting sizeof problems? Please feel free to add them in comments.

C++ example of Linked List implementation

It is debatable if Linked lists are needed in C++, especially because STL can do a very good job for the same functionality for which Linked Lists are required. Nevertheless sometimes it maybe convenient to know linked lists.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include <iostream>
#include <string>
#include <istream>
#include <limits>

using namespace std;

class Node
{
public:
  Node() : next(NULL) {}; //default constructor
  Node(const string& s1) : info(s1), next(NULL) {};
  string info;
  Node* next;
};

Node* getNewNode()
{
  //Lets flush the input buffer first 
  istream& in(cin);
  in.ignore( numeric_limits<std::streamsize>::max(), '\n' );

  //Read the String from console
  cout<<"\tEnter a string: ";
  istreambuf_iterator<char> eos; // end-of-range iterator
  istreambuf_iterator<char> iit (cin.rdbuf()); // stdin iterator
  string s2;
  while (iit!=eos && *iit!='\n') s2+=*iit++;

  //Call the constructor with the input string
  Node* newNode = new Node(s2);

  return newNode;
}

int main()
{
  Node* head = NULL;
  bool contFlag = true;
  char c;

  while(contFlag)
  {
    cout<<"\n\n";
    cout<<"0. Quit"<<endl;
    cout<<"1. Traverse and Print"<<endl;
    cout<<"2. Insert node at the start"<<endl;
    cout<<"3. Insert node at the end"<<endl;
    cout<<"4. Insert after specified number of nodes"<<endl;
    cout<<"5. Remove node from the start"<<endl;
    cout<<"6. Remove node from the end"<<endl;
    cout<<"7. Remove node from a specified number"<<endl;

    cout<<"\nEnter your choice: ";
    cin>>c;

    switch(c)
    {
    case '0':
      contFlag = false;
      break;
    case '1':
      {
        Node* tempNode = head;
        int count = 0;
        while(tempNode)
        {
          cout<<"\tItem "<<count<<" = "<<tempNode->info<<endl;
          tempNode = tempNode->next;
          count++;
        }
      }
      break;
    case '2':
      {
        Node* newNode = getNewNode();
        newNode->next = head;
        head = newNode;
      }
      break;
    case '3':
      {
        Node* newNode = getNewNode();

        Node* endNode = head;
        if(endNode)
        {
          while(endNode->next)
            endNode = endNode->next;
          endNode->next = newNode;
        }
        else //In case its the first element
        {
          head = newNode;
        }
      }
      break;
    case '4':
      {
        Node* tempNode = head;
        if(tempNode)
        {
          unsigned num;
          cout<<"\tInsert after how many nodes? : ";
          cin>>num;
          Node* newNode = getNewNode();

          unsigned count = 1;
          //If less elements are present then insert at the end
          while(tempNode->next && (count < num))
          {
            tempNode = tempNode->next;
            count++;
          }
          newNode->next = tempNode->next;
          tempNode->next = newNode;
        }
        else
        {
          cout<<"\tNo nodes present yet"<<endl;
        }
      }
      break;
    case '5':
      {
        Node* firstNode = head;
        if(firstNode)
        {
          head = firstNode->next;
          delete firstNode;
        }
      }
      break;
    case '6':
      {
        Node* endNode = head;
        if(endNode) //Atleast one element
        {
          Node* endEndNode = endNode->next;
          if(endEndNode) //Atleast 2 elements
          {
            while(endEndNode->next)
            {
              endNode = endEndNode;
              endEndNode = endEndNode->next;
            }
            endNode->next = NULL;
            delete endEndNode;
          }
          else //Only one element
          {
            head = NULL;
            delete endNode;
          }
        }
      }
      break;
    case '7':
      {
        Node* tempNode = head;
        if(tempNode)
        {
          unsigned num;
          cout<<"\tRemove after how many nodes? : ";
          cin>>num;

          unsigned count = 1;
          //If less elements are present then return
          while(tempNode->next && (count < num))
          {
            tempNode = tempNode->next;
            count++;
          }
          if(count == num && tempNode->next && tempNode->next->next)
          {
            Node* nodeToRemove = tempNode->next;
            tempNode->next = nodeToRemove->next;
            delete nodeToRemove;
          }
        }
        else
        {
          cout<<"\tNo nodes present yet"<<endl;
        }
      }
      break;
    default:
      cout<<"Incorrect selection."<<endl;
    }
  }

  return 0;
}

The output is as follows:

You can try more combinations and if you have ideas for improvements please add in the comments section.

Few things to note:

1. This program is for reference and I have not accounted for memory leaks after pressing '0'.

2. For simplicity, getNewNode() is shown as a seperate function. In a real program, it may be better as a method of class Node

3. General Linked Lists use Struct's but in C++, Structs and Classes are nearly the same so its better to use Class.

4. In C++ there is rarely a need to use Linked Lists. Its better to use the STL which already have vectors, stacks, lists, etc.

5. There should be check for memory allocation and try catch blocks that have been ignored for simplicity