c++ pointers and references

01_basic.cpp

#include <bits/stdc++.h>
using namespace std;

int main() {
  int x = 10;
  cout << x << endl;
  cout << &x << endl;
  cout << *(&x) << endl;

  int *y = &x;
  cout << *(y) << endl;

  (*y)++;
  cout << x << endl;

  return 0;
}

02_array.cpp

#include <bits/stdc++.h>
using namespace std;

int main() {
  int ar[10] = {1, 3};

  (*ar)++;
  (*(ar + 1))++;

  int *i = ar;
  (*i) += 10;
  i += 5;
  (*i) += 10;

  long long *l = (long long *)i;
  l++;
  (*(l + 1)) += 7;

  for (auto v : ar) {
    cout << v << ' ';
  }

  return 0;
}

03_vector.cpp

#include <bits/stdc++.h>
using namespace std;

int main() {
  vector<int> vec(10);

  // pointer
  int *p = &(vec[2]);
  (*p) += 10;

  for (size_t i = 0; i < vec.size(); i++)
    vec[i] += 1;

  for (int *i = &(vec[0]); i < &(vec[10]); i++)
    (*i)++;

  // interator
  for (vector<int>::iterator it = vec.begin(); it != vec.end(); ++it)
    (*it)++;

  for (auto it = vec.begin(); it != vec.end(); ++it)
    (*it)++;

  for (int v : vec)
    cout << v << ' ';
  cout << endl;

  for (int i = 0; i <= vec.size(); i++)
    cout << vec[i] << ' ';
  cout << endl;

  return 0;
}

04_fill.cpp

#include <bits/stdc++.h>
using namespace std;

int main() {
  int arr[10];

  fill(arr, arr + 5, 5);       // typesafe
  memset(arr, 1, sizeof(arr)); // slight edge in speed. only used for 0

  // print
  for (int v : arr)
    cout << v << ' ';

  return 0;
}

05_fill_vector.cpp

#include <bits/stdc++.h>
using namespace std;

int main() {
  vector<int> vec(10);

  // fill all
  // works with any standard container that has iterators
  fill(vec.begin(), vec.end() - 5, 5);

  memset(vec.data(), 0, (vec.size() - 7) * sizeof(int));

  // printing
  for (auto v : vec)
    cout << v << ' ';
  cout << endl;

  return 0;
}

06_reference.cpp

#include <bits/stdc++.h>
using namespace std;

int main() {
  int x = 10;
  int &y = x;

  y++;

  cout << x << "," << y;

  return 0;
}

07_fn.cpp

#include <bits/stdc++.h>
using namespace std;

void fn(int x) { // <-- add reference
  x++;
  cout << x << endl;
}

int main() {
  int x = 10;

  fn(x);
  cout << x;
  return 0;
}

08_fn2.cpp

#include <bits/stdc++.h>
using namespace std;

void fn(int *x) {
  (*x)++;
  cout << *x << endl;
}

int main() {
  int x = 10;

  fn(&x);
  cout << x;
  return 0;
}

09_fn_array.cpp

#include <bits/stdc++.h>
using namespace std;

void print(const int arr[], int size) {
  // arr[0]++;
  for (int i = 0; i < size; ++i) {
    cout << arr[i] << " ";
  }
  cout << endl;
}

int main() {
  int ar[10] = {1, 2};
  print(ar, 10);

  return 0;
}

10_fn_vec.cpp

#include <iostream>
#include <vector>

using namespace std;

void fn(vector<int> *vec) {
  cout << "Pointer function: ";
  (*vec)[0] += 1;
  (*vec->begin()) += 1;
  *((*vec).begin()) += 1;
  for (int val : *vec) {
    cout << val << " ";
  }
  cout << endl;
}

void fn2(vector<int> &vec) {
  cout << "Reference function: ";
  *(vec.begin()) += 1;
  for (int val : vec) {
    cout << val << " ";
  }
  cout << endl;
}

void fn3(vector<int> vec) {
  cout << "Value function (cloned): ";
  vec[0]++;
  for (int val : vec) {
    cout << val << " ";
  }
  cout << endl;
}

int main() {
  vector<int> vec = {1, 2, 3, 4, 5};

  fn3(vec); // Pass by value (creates a copy)
  fn(&vec); // Pass by pointer
  fn2(vec); // Pass by reference

  return 0;
}