C++ Programming Code Examples

/* C++ Program to Implement LRU Cache This C++ Program demonstrates the implementation of LRU Cache. */ #include <iostream> #include <cstdlib> #include <cmath> using namespace std; // A Queue Node (Queue is implemented using Doubly Linked List) typedef struct QNode { QNode *prev, *next; unsigned pageNumber; } QNode; // A Queue (A FIFO collection of Queue Nodes) typedef struct Queue { unsigned count; unsigned numberOfFrames; QNode *front, *rear; } Queue; // A hash (Collection of pointers to Queue Nodes) typedef struct Hash { int capacity; QNode **array; } Hash; // A utility function to create a new Queue Node. QNode* newQNode(unsigned pageNumber) { QNode* temp = new QNode; temp->pageNumber = pageNumber; temp->prev = temp->next = NULL; return temp; } // A utility function to create an empty Queue. Queue* createQueue(int numberOfFrames) { Queue* queue = new Queue; queue->count = 0; queue->front = queue->rear = NULL; queue->numberOfFrames = numberOfFrames; return queue; } // A utility function to create an empty Hash of given capacity Hash* createHash(int capacity) { Hash* hash = new Hash; hash->capacity = capacity; hash->array = new QNode* [hash->capacity]; int i; for(i = 0; i < hash->capacity; ++i) hash->array[i] = NULL; return hash; } // A function to check if there is slot available in memory int AreAllFramesFull(Queue* queue) { return queue->count == queue->numberOfFrames; } // A utility function to check if queue is empty int isQueueEmpty( Queue* queue ) { return queue->rear == NULL; } // A utility function to delete a frame from queue void deQueue( Queue* queue ) { if (isQueueEmpty(queue)) return; if (queue->front == queue->rear) queue->front = NULL; QNode* temp = queue->rear; queue->rear = queue->rear->prev; if (queue->rear) queue->rear->next = NULL; free(temp); queue->count--; } // A function to add a page with given 'pageNumber' to both queue and hash void Enqueue(Queue* queue, Hash* hash, unsigned pageNumber) { if (AreAllFramesFull(queue)) { hash->array[queue->rear->pageNumber] = NULL; deQueue(queue); } QNode* temp = newQNode(pageNumber); temp->next = queue->front; if (isQueueEmpty(queue)) queue->rear = queue->front = temp; else { queue->front->prev = temp; queue->front = temp; } hash->array[pageNumber] = temp; queue->count++; } // This function is called when a page with given 'pageNumber' is referenced from cache (or memory). void ReferencePage(Queue* queue, Hash* hash, unsigned pageNumber) { QNode* reqPage = hash->array[pageNumber]; if (reqPage == NULL) Enqueue(queue, hash, pageNumber); else if (reqPage != queue->front) { reqPage->prev->next = reqPage->next; if (reqPage->next) reqPage->next->prev = reqPage->prev; if (reqPage == queue->rear) { queue->rear = reqPage->prev; queue->rear->next = NULL; } reqPage->next = queue->front; reqPage->prev = NULL; reqPage->next->prev = reqPage; queue->front = reqPage; } } // Main int main() { Queue* q = createQueue(4); Hash* hash = createHash( 10 ); ReferencePage(q, hash, 1); ReferencePage(q, hash, 2); ReferencePage(q, hash, 3); ReferencePage(q, hash, 1); ReferencePage(q, hash, 4); ReferencePage(q, hash, 5); cout<<q->front->pageNumber<<" "; cout<<q->front->next->pageNumber<<" "; cout<<q->front->next->next->pageNumber<<" "; cout<<q->front->next->next->next->pageNumber<<" "; return 0; }

/* C++ allows us to allocate the memory of a variable or an array in run time. This is known as dynamic memory allocation. The new operator denotes a request for memory allocation on the Free Store. If sufficient memory is available, new operator initializes the memory and returns the address of the newly allocated and initialized memory to the pointer variable. */ /* Allocate storage space by operator new */ // C++ program code example to illustrate dynamic allocation and deallocation of memory using new and delete #include <iostream> using namespace std; int main () { // Pointer initialization to null int* p = NULL; // Request memory for the variable // using new operator p = new(nothrow) int; if (!p) cout << "allocation of memory failed\n"; else { // Store value at allocated address *p = 29; cout << "Value of p: " << *p << endl; } // Request block of memory // using new operator float *r = new float(75.25); cout << "Value of r: " << *r << endl; // Request block of memory of size n int n = 5; int *q = new(nothrow) int[n]; if (!q) cout << "allocation of memory failed\n"; else { for (int i = 0; i < n; i++) q[i] = i+1; cout << "Value store in block of memory: "; for (int i = 0; i < n; i++) cout << q[i] << " "; } // freed the allocated memory delete p; delete r; // freed the block of allocated memory delete[] q; return 0; }

/* using #include directive in C language */ #include <stdio.h> int main() { /* * C standard library printf function * defined in the stdio.h header file */ printf("I love you Clementine"); printf("I love you so much"); printf("HappyCodings"); return 0; }

/* standard output stream (cout) in C++ language */ #include <iostream> using namespace std; int main() { string str = "Do not interrupt me"; char ch = 'm'; // use cout with write() cout.write(str,6); cout << endl; // use cout with put() cout.put(ch); return 0; }

/* Structure is a collection of variables of different data types under a single name. It is similar to a class in that, both holds a collecion of data of different data types. */ #include <iostream> using namespace std; struct Person { char name[50]; int age; float salary; }; int main() { Person p1; cout << "Enter Full name: "; cin.get(p1.name, 50); cout << "Enter age: "; cin >> p1.age; cout << "Enter salary: "; cin >> p1.salary; cout << "\nDisplaying Information." << endl; cout << "Name: " << p1.name << endl; cout <<"Age: " << p1.age << endl; cout << "Salary: " << p1.salary; return 0; }

/* namespaces in C++ language */ // A C++ code to demonstrate that we can define // methods outside namespace. #include <iostream> using namespace std; // Creating a namespace namespace ns { void display(); class happy { public: void display(); }; } // Defining methods of namespace void ns::happy::display() { cout << "ns::happy::display()\n"; } void ns::display() { cout << "ns::display()\n"; } // Driver code int main() { ns::happy obj; ns::display(); obj.display(); return 0; }

/* write a C program which demonstrate use of if-else-if ladder statement */ /* Program to Print Day Names using Else If Ladder in C++*/ #include <iostream> using namespace std; int main() { int day; cout << "Enter Day Number: "; cin >> day; cout << "Day is "; if (day == 1) cout << "Sunday" << endl; else if (day == 2) cout << "Monday" << endl; else if (day == 3) cout << "Tuesday" << endl; else if (day == 4) cout << "Wednesday" << endl; else if (day == 5) cout << "Thursday" << endl; else if (day == 6) cout << "Friday" << endl; else cout << "Saturday" << endl; return 0; }

/* The free() function in C++ deallocates a block of memory previously allocated using calloc, malloc or realloc functions, making it available for further allocations code example. */ #include <iostream> #include <cstdlib> #include <cstring> using namespace std; int main() { char *ptr; ptr = (char*) malloc(10*sizeof(char)); strcpy(ptr,"Hello C++"); cout << "Before reallocating: " << ptr << endl; /* reallocating memory */ ptr = (char*) realloc(ptr,20); strcpy(ptr,"Hello, Welcome to C++"); cout << "After reallocating: " <<ptr << endl; free(ptr); /* prints a garbage value after ptr is free */ cout << endl << "Garbage Value: " << ptr; return 0; }

/* For Loop Statement in C++ Language */ // C++ program to find the sum of first n natural numbers // positive integers such as 1,2,3,...n are known as natural numbers #include <iostream> using namespace std; int main() { int num, sum; sum = 0; cout << "Enter a positive integer: "; cin >> num; for (int i = 1; i <= num; ++i) { sum += i; } cout << "Sum = " << sum << endl; return 0; }

/* If Else Statement in C++ Language */ #include <iostream> using namespace std; int main () { // local variable declaration: int a = 100; // check the boolean condition if( a < 20 ) { // if condition is true then print the following cout << "a is less than 20;" << endl; } else { // if condition is false then print the following cout << "a is not less than 20;" << endl; } cout << "value of a is : " << a << endl; return 0; }

/* arrays in C++ Language */ #include <iostream> using namespace std; int main() { // initialize an array without specifying size double numbers[] = {7, 5, 6, 12, 35, 27}; double sum = 0; double count = 0; double average; cout << "The numbers are: "; // print array elements // use of range-based for loop for (const double &n : numbers) { cout << n << " "; // calculate the sum sum += n; // count the no. of array elements ++count; } // print the sum cout << "\nTheir Sum = " << sum << endl; // find the average average = sum / count; cout << "Their Average = " << average << endl; return 0; }

/* simple code example by main() function in C++ */ #include <iostream> using namespace std; int main() { int day = 4; switch (day) { case 1: cout << "Monday"; break; case 2: cout << "Tuesday"; break; case 3: cout << "Wednesday"; break; case 4: cout << "Thursday"; break; case 5: cout << "Friday"; break; case 6: cout << "Saturday"; break; case 7: cout << "Sunday"; break; } return 0; }

/* pointer is a variable in C++ that holds the address of another variable */ #include <iostream> using namespace std; int main () { int var = 20; // actual variable declaration. int *ip; // pointer variable ip = &var; // store address of var in pointer variable cout << "Value of var variable: "; cout << var << endl; // print the address stored in ip pointer variable cout << "Address stored in ip variable: "; cout << ip << endl; // access the value at the address available in pointer cout << "Value of *ip variable: "; cout << *ip << endl; return 0; }