Computer Science:Online Resources

1. Object-Oriented Programming in Python

Queue : Array Implementation in C

#include <stdio.h>
#define QUEUE_LENGTH 50
struct queue
{
    int element[QUEUE_LENGTH];
    int front,rear,choice,x,y;
};
void traverse(struct queue q)
 {  printf("The elements of the queue are\n");
     for(int i=0;i<=q.rear;i++)
     {
         printf("%d\n",q.element[i]);
     }
 }
void add(struct queue *p,int y)
{
    if((*p).rear<QUEUE_LENGTH)
    {   (*p).rear +=1;
        (*p).element[(*p).rear]=y;
        printf("rear =  %d\n",(*p).rear);
        printf("type -1 to exit\n");
        scanf("%d",&y);
        if(y==(-1))
        {
            return;
        }
        add(p,y);
    }
    else
    {
        printf("Queue overflow\n");
    }
}
void delete(struct queue *p)
{
    int x=0,y=0;
    if((*p).front>(*p).rear)
    {
        printf("Queue empty\n");
    }
    else
    {
        x=(*p).element[(*p).front];
        (*p).element[(*p).front]=0;
        (*p).front=(*p).front+ 1;
    }
    printf("type 1 to delete or 2 to exit\n");
        scanf("%d",&y);
        if(y==(2))
        {
            return ;
        }
        if(y==(1))
        {
            traverse(*p);
            printf("%d is deleted\n",(*p).element[(*p).front]-1);
            delete(p);

        }
}
int main()
{   int choice=0,x=0;
    struct queue q;
    q.rear= -1,q.front=0;
        printf("\nEnter element to be added:\n");
        scanf("%d",&x);
        add(&q,x);
        traverse(q);
        delete(&q);
        printf("Deletion completed \n");
    return 0;
}

Output:

$gcc -o main *.c
$main
 
Enter element to be added:
1
rear =  0
type -1 to exit
2
rear =  1
type -1 to exit
3
rear =  2
type -1 to exit
4
rear =  3
type -1 to exit
5
rear =  4
type -1 to exit
6
rear =  5
type -1 to exit
7
rear =  6
type -1 to exit
-1
The elements of the queue are
1
2
3
4
5
6
7
type 1 to delete or 2 to exit
The elements of the queue are
0
2
3
4
5
6
7
1 is deleted
type 1 to delete or 2 to exit
The elements of the queue are
0
0
3
4
5
6
7
2 is deleted
type 1 to delete or 2 to exit
The elements of the queue are
0
0
0
4
5
6
7
3 is deleted
type 1 to delete or 2 to exit
Deletion completed 

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Java Tutorial

http://tutorials.jenkov.com/java/access-modifiers.html

C++ : ' string ' Data type

#include<iostream>
#include<string>
using namespace std;
int main(){
string arr[3][3] = {"Blue", "Red", "Orange", "night","ok","that","is","good","bye"};

for(int i=0;i<3;i++)
{

    for(int j=0;j<3;j++)
    {

        cout<< arr[i][j]<<" "<<i<<" "<<j<<endl;
       
    }

}
return 1;
}

Flow of values of pointers in a Singly Linked-list as new nodes get added from front

#include<stdio.h>
#include<stdlib.h>
struct Node{
int value;
struct Node * next;
};
int insertNode(struct Node** head,int value){
    printf("Insert Node %d\n",value);
    struct Node* newNodePtr = (struct Node*)malloc(sizeof(struct Node));
    newNodePtr->value=value;
    newNodePtr->next=*head; // Now the 'next' of the NEW NODE holds what head held originally = NULL
    printf(" address in newNodePtr = %d = address OF the NEW NODE\n",newNodePtr);
    printf(" address in newNodePtr->next = %d \n",newNodePtr->next);
    printf(" address in *head = %d \n",*head);
    printf(" address in head = %d \n",head);
    *head=newNodePtr; // I am changing where head is POINTING TO, it now POINTS TO 'newNodePtr'
    // i.e. to the NEW NODDE (now holds the address of a POINTER pointing to the NEW NODE
    printf("Finally address OF head = %d \n",head);
    printf("Finally address in head = *head = %d = address OF the NEW NODE\n",*head);
    return 1;
}
void PrintList(struct Node* head){
        while(head){
        printf("value in nodes is %d \n",head->value);
        head = head->next;
        }
}
int main(){
    int a =10;
    int * p = &a; // 'p' points to 'a'
  struct Node * head = NULL;
   printf("In main, address IN 'head' = %d i.e. head POINTS TO NULL\n",head);
   printf("In main, But 'head' has ITS OWN ADDRESS (address of head = '&head') = %d \n",&head);
   printf("This address OF head '&head' = %d UNIQUELY IDENTIFIES this LIST and remains",&head);
   printf("UNCHANGED throughout\n");
   printf("In main, value at address of head '*(&head) = %d = address in 'head'\n",*(&head));
   printf("This means address IN 'head' == '*(&head)'\n");
   printf("NOTE: 'Node ** head == '&head', POINTER-2-POINTER i.e. ADRRESS of a POINTER\n");
   printf("Therefore, '*heaad' == Address held by 'head',i.e. where the head is POINTING TO");
   printf(" p = %d\n",p);
   printf(" &a = %d\n",&a);
   printf(" &p = %d\n",&p);
   printf(" *(&p) = %d\n",*(&p));
   printf(" *p = %d\n",*p);
   printf("(1) This means p == *(&p), where 'p' is any POINTER\n");
   printf("(2) This means if you print 'p' you will get '&a', because p=&a\n");
   printf("\nSee how the values of newNodePtr, newNodePtr->next\n");
   printf("addresses head holds(points to) changes, BUT  the address OF HEAD\n");
   printf("remains the SAME with each call to insertNode\n\n");
  int arr[5]={1,2,3,4,5};
    int i;
    for(i=0;i<5;i++){
     insertNode(&head,arr[i]);
    }
     PrintList(head);
    return 0;
}


Output:

$gcc -o main *.c
$main
In main, address IN 'head' = 0 i.e. head POINTS TO NULL
In main, But 'head' has ITS OWN ADDRESS (address of head = '&head') = -1625641784 
This address OF head '&head' = -1625641784 UNIQUELY IDENTIFIES this LIST and remainsUNCHANGED throughout
In main, value at address of head '*(&head) = 0 = address in 'head'
This means address IN 'head' == '*(&head)'
NOTE: 'Node ** head == '&head', POINTER-2-POINTER i.e. ADRRESS of a POINTER
Therefore, '*heaad' == Address held by 'head',i.e. where the head is POINTING TO p = -1625641768
 &a = -1625641768
 &p = -1625641776
 *(&p) = -1625641768
 *p = 10
(1) This means p == *(&p), where 'p' is any POINTER
(2) This means if you print 'p' you will get '&a', because p=&a

See how the values of newNodePtr, newNodePtr->next
addresses head holds(points to) changes, BUT  the address OF HEAD
remains the SAME with each call to insertNode

Insert Node 1
 address in newNodePtr = 10371104 = address OF the NEW NODE
 address in newNodePtr->next = 0 
 address in *head = 0 
 address in head = -1625641784 
Finally address OF head = -1625641784 
Finally address in head = *head = 10371104 = address OF the NEW NODE
Insert Node 2
 address in newNodePtr = 10371136 = address OF the NEW NODE
 address in newNodePtr->next = 10371104 
 address in *head = 10371104 
 address in head = -1625641784 
Finally address OF head = -1625641784 
Finally address in head = *head = 10371136 = address OF the NEW NODE
Insert Node 3
 address in newNodePtr = 10371168 = address OF the NEW NODE
 address in newNodePtr->next = 10371136 
 address in *head = 10371136 
 address in head = -1625641784 
Finally address OF head = -1625641784 
Finally address in head = *head = 10371168 = address OF the NEW NODE
Insert Node 4
 address in newNodePtr = 10371200 = address OF the NEW NODE
 address in newNodePtr->next = 10371168 
 address in *head = 10371168 
 address in head = -1625641784 
Finally address OF head = -1625641784 
Finally address in head = *head = 10371200 = address OF the NEW NODE
Insert Node 5
 address in newNodePtr = 10371232 = address OF the NEW NODE
 address in newNodePtr->next = 10371200 
 address in *head = 10371200 
 address in head = -1625641784 
Finally address OF head = -1625641784 
Finally address in head = *head = 10371232 = address OF the NEW NODE
value in nodes is 5 
value in nodes is 4 
value in nodes is 3 
value in nodes is 2 
value in nodes is 1 

MEAN stack: Integrating Angular with Node

Good link Mean stack tutorial

Icon: How to launch your C/C++/Java programs from icons in desktop/start menu in Windows

These links explain it :
1. How-do-i-give-a-c-program-an-icon
2. How-to-run-java-programs-by-clicking-on-their-icon-on-windows