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