This code is an implementation and test driver of a doubly linked list. This list is pointer based and uses dynamic memory.

Sorted Doubly Linked List with Insertion and Deletion

#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;

class Dllist
{
 private:
 typedef struct Node
 {
 string name;
 Node* next;
 Node* prev;
 };
 Node* head;
 Node* last;
 public:
 Dllist()
 {
 head = NULL;
 last = NULL;
 }
 bool empty() const { return head==NULL; }
 friend ostream& operator<<(ostream& ,const Dllist& );
 void Insert(const string& );
 void Remove(const string& );
};

void Dllist::Insert(const string& s)
{
 // Insertion into an Empty List.
 if(empty())
 {
 Node* temp = new Node;
 head = temp;
 last = temp;
 temp->prev = NULL;
 temp->next = NULL;
 temp->name = s;
 }
 else
 {
 Node* curr;
 curr = head;
 while( s>curr->name && curr->next != last->next) curr = curr->next;

 if(curr == head)
 {
 Node* temp = new Node;
 temp->name = s;
 temp->prev = curr;
 temp->next = NULL;
 head->next = temp;
 last = temp;
 //  cout<<" Inserted "<<s<<" After "<<curr->name<<endl;
 }
 else
 {
 if(curr == last && s>last->name)
 {
 last->next = new Node;
 (last->next)->prev = last;
 last = last->next;
 last->next = NULL;
 last->name = s;
 //  cout<<" Added "<<s<<" at the end "<<endl;
 }
 else
 {
 Node* temp = new Node;
 temp->name = s;
 temp->next = curr;
 (curr->prev)->next = temp;
 temp->prev = curr->prev;
 curr->prev = temp;
 //  cout<<" Inserted "<<s<<" Before "<<curr->name<<endl;
 }
 }
 }
}

ostream& operator<<(ostream& ostr, const Dllist& dl )
{
 if(dl.empty()) ostr<<" The list is empty. "<<endl;
 else
 {
 Dllist::Node* curr;
 for(curr = dl.head; curr != dl.last->next; curr=curr->next)
 ostr<<curr->name<<" ";
 ostr<<endl;
 ostr<<endl;
 return ostr;
 }
}

void Dllist::Remove(const string& s)
{
 bool found = false;
 if(empty())
 {
 cout<<" This is an empty list! "<<endl;
 return;
 }
 else
 {
 Node* curr;
 for(curr = head; curr != last->next; curr = curr->next)
 {
 if(curr->name == s)
 {
 found = true;
 break;
 }
 }
 if(found == false)
 {
 cout<<" The list does not contain specified Node"<<endl;
 return;
 }
 else
 {
 // Curr points to the node to be removed.
 if (curr == head && found)
 {
 if(curr->next != NULL)
 {
 head = curr->next;
 delete curr;
 return;
 }
 else
 {
 delete curr;
 head = NULL;
 last = NULL;
 return;
 }
 }
 if (curr == last && found)
 {
 last = curr->prev;
 delete curr;
 return;
 }
 (curr->prev)->next = curr->next;
 (curr->next)->prev = curr->prev;
 delete curr;
 }
 }
}

int main()
{
 Dllist d1;
 int ch;
 string temp;
 while(1)
 {
 cout<<endl;
 cout<<" Doubly Linked List Operations "<<endl;
 cout<<" ------------------------------"<<endl;
 cout<<" 1. Insertion "<<endl;
 cout<<" 2. Deletion "<<endl;
 cout<<" 3. Display "<<endl;
 cout<<" 4. Exit "<<endl;
 cout<<" Enter your choice : ";
 cin>>ch;
 switch(ch)
 {
 case 1: cout<<" Enter Name to be inserted : ";
 cin>>temp;
 d1.Insert(temp);
 break;
 case 2: cout<<" Enter Name to be deleted : ";
 cin>>temp;
 d1.Remove(temp);
 break;
 case 3: cout<<" The List contains : ";
 cout<<d1;
 break;
 case 4: system("pause");
 return 0;
 break;
 }
 }

This code is a simple example of how to safely open a text file in C++. Notice the very important check that the file was opened correctly. This covers a range of errors,  most commonly file not found.

// Read integers from file and print sum.

#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>

using namespace std;

int main() {
 int sum = 0;
 string word;
 ifstream inFile;

 inFile.open("test.txt");
 if (!inFile) {
 cout << "Unable to open file";
 exit(1); // terminate with error
 }

 while (inFile >> word) {
 cout << word << " ";
 }

 inFile.close();

 return 0;
}

this snippet of code is an alternative to system(“pause”) in MS Visual Studio.

/*
* File:   SystemPause.cpp
* Author: B Turley
*
* This function can be used as a substitute for 'system("pause")'
* in Microsoft Visual Studio
*
* Created on November 10, 2009, 1:17 AM
*/

#include <iostream>
#include <limits>
using namespace std;

void pause()
{
cout<<"Press any key to Continue...";
cin.sync();
cin.ignore(numeric_limits<streamsize> ::max(), '\n');
}

int main(int argc, char** argv) {

pause();

return (0);
}

This little piece of code can convert a string of decimal characters into an integer value.  If you seek to convert a string into a double, see this post.

/*
 * A function to convert a string into an integer
 */

#include <string>

int StringToInt (std::string str)
{
    int total = 0;
    int length = str.length(); // the length of the string
    int x = 1; // this is our multiplier, used to convert each digit into tens, units, etc
    for (int i = 1; i < str.length(); i++)
        x *= 10; // initialise x correctly

    for (int i = 0; i < length; i++)
    { // loop through the string
        // 48 is the base value (ASCII)
        // multiply it by x to get it into tens, units, etc
        total += (static_cast <int> (str[i]) - 48) * x;
        x /= 10; // divide x by 10, to reduce the units by one
    }

    return total; // return the value as an integer
}

/** EXAMPLE USAGE **/
#include <iostream>
int main ()
{
    int t = StringToInt("1234") + 300;
    std::cout < < t; // should be 1534 (1234 + 300 = 1534)

    std::cin.get ();
    return EXIT_SUCCESS;
}