« Pointers And Arrays

Understand similarities between pointers and arrays

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1int arr[10];
2cout << "arr: " << arr << endl;
3cout << "&arr[0]: " << &arr[0] << endl;

This will create 40 bytes storage for array. a is basically name for this 40 bytes. In symbol table there will be a entry of a = starting address of this 40 bytes which is same as address of arr[0] i.e. &arr[0]. So arr can be treated almost exactly like a pointer.

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1cout << "*arr: " << (*arr) << endl;
2arr[0] = 5;
3arr[1] = 10;
4cout << "*arr: " << (*arr) << endl;
5cout << "*(arr+1): " << (*(arr + 1)) << endl;
6cout << "1[arr]: " << 1 [arr] << endl;

So, arr[i] and *(arr+i) are same. i[arr] and *(i+arr) are also same. So arr[i] and *(arr+i) and i[arr] are all same

Understand dissimilarities between pointers and arrays

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1cout << "sizeof(arr): " << sizeof(arr) << endl;
2cout << "arr: " << arr << endl;
3cout << "&arr: " << &arr << endl;

Although arr can be treated as pointer but there are couple of differences. sizeof(arr) = 40 as in symbol table its mentioned that it is a array of size 10. But sizeof(pointer) = 8. All these difference is because, for pointers another 8 byte memory is created for it and saved to the symbol table, but for arrays no extra storage is created. In symbol table arr = address of array is stored.

arr and &arr prints same but pointer and &pointers prints different. Reason: for storing pointers another storage is created but not for arrays(arrays are just entered in the symbol table).

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1//arr = arr + 3; //this will give error

Array can not be reassigned. Something entered in a symbol table cannot be changed.

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1int *ptr = arr;
2cout << "ptr " << ptr << endl;

You can't do array = pointer but you can do pointer = array

Final Code

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1#include <iostream>
2#include <iomanip>
3#include <algorithm>
4#include <string>
5#include <cstring>
6#include <vector>
7#include <cmath>
8#include <map>
9#include <climits>
10// climits for INT_MIN
11#include <unordered_map>
12using namespace std;
13int main()
14{
15    int arr[10];
16    /*
17    This will create 40 bytes storage for array
18    _________________________________________________________
19    |________________________________________________________|
20
21    a is basically name for this 40 bytes
22    in symbol table there will be a entry of a = starting address of this 40 bytes which is same as address of arr[0] i.e. &arr[0]
23    */
24
25    cout << "arr: " << arr << endl;
26    cout << "&arr[0]: " << &arr[0] << endl;
27    // So arr can be treated almost exactly like pointer
28
29    cout << "*arr: " << (*arr) << endl;
30    arr[0] = 5;
31    arr[1] = 10;
32    cout << "*arr: " << (*arr) << endl;
33    cout << "*(arr+1): " << (*(arr + 1)) << endl;
34
35    cout << "1[arr]: " << 1 [arr] << endl;
36
37    cout << "sizeof(arr): " << sizeof(arr) << endl;
38    cout << "arr: " << arr << endl;
39    cout << "&arr: " << &arr << endl;
40
41    // arr = arr + 3; array can not be reassigned.
42
43    int *ptr = arr;
44    cout << "ptr " << ptr << endl;
45    // You can't do array = pointer but you can do pointer = array
46
47    return 0;
48}