pointers

1Variable is used to store value
2Pointer is used to store addresss of value

1#include <stdio.h>
2
3int main () {
4
5   int  var = 20;   /* actual variable declaration */
6   int  *ip;        /* pointer variable declaration */
7
8   ip = &var;  /* store address of var in pointer variable*/
9
10   printf("Address of var variable: %x\n", &var  );
11
12   /* address stored in pointer variable */
13   printf("Address stored in ip variable: %x\n", ip );
14
15   /* access the value using the pointer */
16   printf("Value of *ip variable: %d\n", *ip );
17
18   return 0;
19}

1/*
2**use of pointers is that here even if we change the value of c since the adderss is
3* of c is assigned to pc it *pc will also get modified*/
4int* pc, c;
5c = 5;
6pc = &c;
7*pc = 1;
8printf("%d", *pc);  // Ouptut: 1
9printf("%d", c);    // Output: 1
10

1#include <stdio.h>
2int main() {
3   int c = 5;
4   int *p = &c;
5
6   printf("%d", *p);  // 5
7   return 0; 
8}

1int* pc, c, d;
2c = 5;
3d = -15;
4
5pc = &c; printf("%d", *pc); // Output: 5
6pc = &d; printf("%d", *pc); // Ouptut: -15

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}