Write a program to Implement a Queue in C++

User is asked to Insert into.. Delete from or Display the entire queue..

Select To use this code as it is.. select and copy paste this code into code.cpp file :)

1. #include<stdio.h> 


2. #include<conio.h> 


3. #include<process.h> 


4. int queue[5]; 


5. long front,rear; 


6. void initqueue(); 


7. void display(); 


8. void main() 


9. { 


10. int choice,info; 


11. clrscr(); 


12. while(1) 


13. { 


14. clrscr(); 


15. printf(" MENU \n"); 


16. printf("1.Insert an element in queue\n"); 


17. printf("2.Delete an element from queue\n"); 


18. printf("3.Display the queue\n"); 


19. printf("4.Exit!\n"); 


20. printf("Your choice: "); 


21. scanf("%i",&choice); 


22. //Coding by: Snehil Khanor  


23. //http://WapCPP.blogspot.com  


24. switch(choice) 


25. { 


26. case 1:if(rear<4) 


27. { 


28. printf("enter the number: "); 


29. scanf("%d",&info); 


30. if (front==-1) 


31. { 


32. front=0; 


33. rear=0; 


34. } 


35. else 


36. rear=rear+1; 


37. queue[rear]=info; 


38. } 


39. else 


40. printf("queue is full"); 


41. getch(); 


42. break; 


43. case 2: int info; 


44. if(front!=-1) 


45. { 


46. info=queue[front]; 


47. if(front==rear) 


48. { 


49. front=-1; 


50. rear=-1; 


51. } 


52. else 


53. front=front+1; 


54. printf("no deleted is = %d",info); 


55. } 


56. else 


57. printf("queue is empty"); 


58. getch(); 


59. break; 


60. case 3: display(); 


61. getch(); 


62. break; 


63. case 4: exit(1); 


64. break; 


65. default:printf("You entered wrong choice!"); 


66. getch(); 


67. break; 


68. } 


69. } 


70. } 


71. void initqueue() 


72. { 


73. front=rear=-1; 


74. } 


75. void display() 


76. { 


77. int i; 


78. for(i=front;i<=rear;i++) 


79. printf("%i\n",queue[i]); 


80. } 

Simple Function Pointers example

This example shows how function pointers work. There is also an example of how priority queues work.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This program intents to show the use of function pointers
//This program also uses priority queues
#include<iostream>
#include<queue>

using namespace std;

typedef int (*fpRegCb)(int* i_p, int index);

int funcA(int *val, int index)
{
  cout<<"Func A: index = "<<index<<"   val = "<<*val<<endl;
  return (*val + 10);
}

int funcB(int *val, int index)
{
  cout<<"Func B: index = "<<index<<"   val = "<<*val<<endl;
  return (*val + 15);
}

class someSimpleListType
{
private:
  someSimpleListType(); //This cant be used
public:
  int index;
  int *value;
  fpRegCb callback;
  someSimpleListType(fpRegCb cb, int *val, int idx):value(val),index(idx)
  {
    callback = cb;
  };
  //< operator is overloaded for use with priority queues. This will
  //decide the priority of the new element, where it should be placed
  const bool operator <(const someSimpleListType& sLT) const
  {
    return (index < sLT.index);
  }
};

priority_queue <someSimpleListType> someSimpleList;

int main()
{
  int index=0;
  int *a=new int(22);
  int *b=new int(37);
  int *c=new int(62);

  //The higher the priority, higher it is in the queue
  someSimpleList.push(someSimpleListType(funcA, a, index++));
  someSimpleList.push(someSimpleListType(funcB, b, index++));
  someSimpleList.push(someSimpleListType(funcB, c, index++));
  //The last push will end up top of queue as index(priority) is greatest

  //Lets get all the elements from the list and process them
  cout<<"Test 1"<<endl;
  while(!someSimpleList.empty())
  {
    someSimpleListType &sLT = someSimpleList.top();
    cout<<"Callback["<<sLT.index<<"] = "<<sLT.callback(sLT.value,sLT.index)<<endl;
    someSimpleList.pop();
  }

  //Since the priority queue is now empty, push some more elements
  someSimpleList.push(someSimpleListType(funcA, a, index++));
  someSimpleList.push(someSimpleListType(funcB, b, index++));
  someSimpleList.push(someSimpleListType(funcB, c, index++));

  //This time we will only process funcB and ignore funcA
  cout<<endl<<"Test 2"<<endl;
  while(!someSimpleList.empty())
  {
    someSimpleListType &sLT = someSimpleList.top();
    if(sLT.callback == funcB)
    {
      cout<<"Callback["<<sLT.index<<"] = "<<sLT.callback(sLT.value,sLT.index)<<endl;
    }
    someSimpleList.pop();
  }

  return 0;
}