Pointers

#include<bits/stdc++.h>
using namespace std;
void arrpass(int *a, int n)//address sedn kiya toh receive bhi pointer ne kiya
{
	cout << a << endl;
	cout << *a << endl; //value at a[0]
	a[0] = 100; //or *a=100 is same
	// as the change is made at the address of base index it will reflect in the originla array also
}
void vectorpassbyvalue(vector<int> a)
{
	a[0] = 100;
}
void vectorpassbyreference(vector<int>&a)
{
	a[0] = 200;
}
int main()
{
	/////////////////////////////////////part 1 basics of pointers
	// and double pointers
	// int i = 10;//intialise the value 10 at i
	// int *p = &i;//stre th adrress of i in pointer variable
	// cout << p << endl; //address of i
	// cout << *p << endl; //value of i
	// (*p)++; //or i++ is same but *p++==incorrect and (*p)++==correct
	// //after this no change in p but will change value of i
	// cout << i << endl;//11
	// // cout << *(p++) << endl;//11
	// // cout << (*p++) << endl;//garbage


	// int **q = &p; //q will store addrees of p
	// cout << q << endl; //address of p;
	// cout << *q << endl; //value stored at p ie address of i
	// cout << **q << endl; //value of i

	// cout << **(q++) << endl;
	// // cout << (**q++) << endl;
	// cout << endl << endl << endl;



// ///////////////pointers will not point to garbage value
// 	int a;
// 	int *b;
// 	cout << a << endl; //garbage at i
// 	cout << b << endl; //garbage at pointer p
// 	cout << *b << endl; // may throw error as pointer is having address of garbage and
// 	//value at that garbage may or may not exist
// 	cout << endl << endl << endl;



//////////////array as pointers
	// //arr[i],*(arr+i),i[arr];
	// int arr[10];
	// arr[0] = 5, arr[1] = 10;
	// cout << arr << endl;//adrres of a[0];
	// cout << (*arr) << endl;//value at arr[0]
	// cout << *(arr + 1) << endl;//value at arr[1];
	// cout << 0[arr] << endl;
	// cout << endl << endl << endl;



// //////////differenec in arrray and pointers
// 	int val = 10;
// 	int *pointer = &val;
// 	cout << pointer << endl; //address of val
// 	cout << *pointer << endl; //value at address of pointer
// 	*pointer++;//etc will change val
// 	pointer = pointer + 1; //will change the address(value) stored at pointer by 4 bytes

// 	int checkarr[10];
// 	cout << checkarr << endl; //address at 0th index
// 	cout << &checkarr[0] << endl;
// 	cout << *(checkarr) << endl; //value at 0th index


// 	//////////1st point
// 	pointer = pointer + 1; //is valid
// 	// checkarr = checkarr + 1; //not valid we can not reassign address in symbol table
// 	pointer = checkarr + 1 ;// we can do this
// 	cout << endl << endl << endl;


/////////////character and pointers
	// char c1 = 'a';
	// char* pc = &c1;
	// cout << c1 << endl;
	// cout << pc << endl;//instead of printing address of c1 it will print c1
	// cout << *pc << endl;

	// char str[] = "abc";
	// cout << str << endl;//instead of printing address of str[0],print whole string
	// char *pcc = &str[0];
	// cout << pcc << endl;
	// cout << *pcc << endl;


/////////arrays and vectors pass by value and pass by reference
	int arraybyreference[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
	cout << arraybyreference << endl; //address of a[0]
	cout << &arraybyreference[0] << endl;//address of a[0]
	cout << *arraybyreference << endl;//value stored at address of a[0]
	arrpass(arraybyreference, 10);//sending the address of a[0]
	for (int i = 0; i < 10; i++)
	{
		cout << arraybyreference[i] << " ";
	}

	////while passing array through any function we always pass address
	///of its 0th index and it wil be received by pointer in function
	///and change in fun will reflect in maine array
	///array can only be passed via call by reference change in fun will reflect in main.
	cout << endl << endl << endl;


// 	////in case of vectors it can be passed in both ways;
// 	vector<int> vec{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
// 	vectorpassbyvalue(vec);
// 	for (int i = 0; i < 10; i++) { cout << vec[i] << " ";} cout << endl; //no change in main vector
// 	vectorpassbyreference(vec);
// 	for (int i = 0; i < 10; i++) { cout << vec[i] << " ";} cout << endl; //change in main vector
// 	cout << endl << endl << endl;



// ////////////reference variable
// // same memory me pahucne ke do alag alag raste
// //declaration of reference variable should be done at the time of initialisation
// 	int original = 10;
// 	int& referenceoriginal = original;
// 	original++;
// 	cout << original << endl;
// 	cout << referenceoriginal << endl;
// 	cout << endl << endl << endl;



// /////////dynamic memory allocation
// 	//in variables
// 	int *variabledynamic = new int;
// 	cout << variabledynamic << endl;
// 	*variabledynamic = 10;
// 	cout << *variabledynamic << endl;

// 	//inarrays
// 	int* arraydynamic = new int[10];
// 	cout << arraydynamic << endl;
// 	arraydynamic[0] = 100;
// 	cout << *arraydynamic << endl;
// 	cout << arraydynamic[0] << endl;
// 	cout << endl << endl << endl;





}

//1 pointers in variables
//2 pointers in arrays
//3 pointers in char
//4 pointers in char array
//5 pass variable in a fun (by value or by reference)
//6 pass array in a fun (only done by reference)
//7 pass vector in a fun (by value or by reference)
//8 double pointers
//9 type casting (implicit and explicit)
//10 reference variable
//11 dynamic memory allocation in variables and arrays.