pointer in c 2b 2b

1#include <iostream>
2using namespace std;
3int main(){
4   //Pointer declaration
5   int *p, var=101;
6 
7   //Assignment
8   p = &var;
9
10   cout<<"Address of var: "<<&var<<endl;
11   cout<<"Address of var: "<<p<<endl;
12   cout<<"Address of p: "<<&p<<endl;
13   cout<<"Value of var: "<<*p;
14   return 0;
15}

1#include <iostream>
2
3using namespace std;
4
5int main () {
6   int  var = 20;   // actual variable declaration.
7   int  *ip;        // pointer variable 
8
9   ip = &var;       // store address of var in pointer variable
10
11   cout << "Value of var variable: "; 
12   cout << var << endl; //Prints "20"
13
14   // print the address stored in ip pointer variable
15   cout << "Address stored in ip variable: ";
16   cout << ip << endl; //Prints "b7f8yufs78fds"
17
18   // access the value at the address available in pointer
19   cout << "Value of *ip variable: ";
20   cout << *ip << endl; //Prints "20"
21
22   return 0;
23}

1#include <iostream>
2
3using namespace std;
4// isualize this on http://pythontutor.com/cpp.html#mode=edit
5int main()
6{
7   double* account_pointer = new double;
8   *account_pointer = 1000;
9   cout << "Allocated one new variable containing " << *account_pointer
10      << endl;
11   cout << endl;
12
13   int n = 10;
14   double* account_array = new double[n];
15   for (int i = 0; i < n; i++)
16   {
17      account_array[i] = 1000 * i;
18   }   
19   cout << "Allocated an array of size " << n << endl;
20   for (int i = 0; i < n; i++)
21   {
22      cout << i << ": " << account_array[i] << endl;
23   }
24   cout << endl;
25
26   // Doubling the array capacity 
27   double* bigger_array = new double[2 * n];
28   for (int i = 0; i < n; i++)
29   {
30      bigger_array[i] = account_array[i];
31   }
32   delete[] account_array; // Deleting smaller array
33   account_array = bigger_array;
34   n = 2 * n;
35
36   cout << "Now there is room for an additional element:" << endl;
37   account_array[10] = 10000;
38   cout << 10 << ": " << account_array[10] << endl;    
39   
40   delete account_pointer;
41   delete[] account_array; // Deleting larger array
42   
43   return 0;
44}

1// Variable is used to store value
2int a = 5;
3cout << a; //output is 5
4
5// Pointer is used to store address of variable
6int a = 5;
7int *ab;
8ab = &a; //& is used get address of the variable
9cout << ab; // Output is address of variable

1#include <iostream>
2using std::cout;
3
4int main() {
5  /* 
6  Some things to keep in mind:
7  	-you shouldn't circumvent the type system if you are creating raw ptrs
8  	and don't need to "type pun" or cast (don't use void ptrs)
9    -ptr types only reference memory (which are integers), not actual data, thus
10    they should not be treated as data types
11    char* is just 1 byte of mem, int* is just 4 bytes of mem, etc
12    - '*' means that you are creating a pointer which "points" to the mem address
13    of a variable
14    - '&', in this case, means "get the mem address of this variable"
15  */
16  
17  void* ptr; // a pointer that doesn't reference a certain size of memory
18  int* int_ptr; // a pointer that points to data with
19  				// only 4 bytes of memory (on stack)
20  
21  int a = 5; // allocates 4 bytes of mem and stores "5" there (as a primitive)
22  ptr = &a; // can only access the memory address of 'a' (not the data there)
23  
24  int b = 45; 
25  int_ptr = &b; // can access both memory address and data of 'b'
26  
27  cout << ptr << "\n"; // prints mem address of 'a'
28  /*cout << *ptr << "\n"; <- this will error out; a void ptr cannot be 
29  							 derefrenced */
30  cout << *(int*)ptr << "\n"; // type punning to get around void ptr (extra work)
31  
32  cout << int_ptr << "\n"; // mem address of b
33  cout << *int_ptr << "\n"; // data stored at b
34  
35  /* -- OUTPUTS -- */
36  /*
37  	some memory address (arbitrary) which contains 05 00 00 00 as its data
38  	5
39    some memory address (arbitrary) which contains 2D 00 00 00 as its data
40    45
41  */
42  
43  return 0; // you only need this if "main" isnt the linker entry point
44  			// you also don't care
45  
46  // ur also probably wondering why I didn't using namespace std... cherno
47}

1int* pointVar, var;
2var = 5;
3
4// assign address of var to pointVar
5pointVar = &var;
6
7// access value pointed by pointVar
8cout << *pointVar << endl;   // Output: 5
9
10In the above code, the address of var is assigned to the pointVar pointer.
11We have used the *pointVar to get the value stored in that address.