Miscellaneous

• oop
• derived from c
• c with classes, but now it's much more

• low level access to memory

• Advantages

  • fast
  • more low level access
• Disadvantages
  • memory leaks
  • oop drawbacks, due to multiple inheritance
  • porting to other platform is time consuming

Common Mistakes

• Reading bullschildt http://www.lysator.liu.se/c/schildt.html
• https://stackoverflow.com/questions/2934904/order-of-evaluation-in-c-function-parameters
• https://stackoverflow.com/questions/17358445/why-does-right-shifting-negative-numbers-in-c-bring-1-on-the-left-most-bits
• https://stackoverflow.com/questions/562303/the-definitive-c-book-guide-and-list/579795#579795
• https://stackoverflow.com/questions/2397984/undefined-unspecified-and-implementation-defined-behavior

OOP in C++

• Classes
  • templates for objects
  • when a class is instantiated it becomes a object
• Object
  • instance of the class

FAQ and common misconceptions

• C++ is C with classes
  • although this is correct but this does not means all the C features are available in C++ also
  • you should follow C++ standard and not something that works in a particular compiler
  • #include<bits/stdc++.h> this is g++ specific library, so if you use it on some other compiler it will not work.
  • other difference are in initialization of variable sized array, in g++ the declaration int a[v] = {0}; will work but it will not work in every compiler, because it is not in C++ specification. C++ don't support variable length arrays.

• out of scope vector

  • https://stackoverflow.com/questions/59071549/can-i-keep-vector-data-even-after-out-of-scope

  • https://stackoverflow.com/questions/15704565/efficient-way-to-return-a-stdvector-in-c

  • cpp vector<int> getNo(){ vector<int> ans = {1,2,3}; return ans; }

  • here when the function getNo is called it creates a vector and when it return it returns a copy of vector and not the actual created vector ans. OR it can be moved too, instead of returning, some other compiler optimization are also done.

  • how to pass a 2-D matrix
  • https://stackoverflow.com/questions/8767166/passing-a-2d-array-to-a-c-function
  • often time you will notice some online contest giving you arrays instead if vectors
  • this is confusing because we are not able to see further implementation detail.

  • the most confusing one is int **arr passed in function

  • cpp int arr[12][12]; void pass(int a[][10]){}

  • cpp int *arr[10]; for(int i=0;i<10;i++) arr[i] = new int[10]; void pass(int *a[10]){}

  • cpp // this is the way they pass these function online int **arr; arr = new int *[10]; // arr is an array of 10 (pointers to arr) for(int i=0;i<10;i++) arr[i] = new int[10]; void pass(int **arr){}

• how to create a variable sized array

  • https://stackoverflow.com/questions/15013077/arrayn-vs-array10-initializing-array-with-variable-vs-numeric-literal

Typecasting error

• first store result in a variable then use it inside if else because of type conversions, note that size return unsigned numbers for all containers.

long n;
long temp;

// this will give -1 if n = temp*s.length()
long answer = n - temp * s.length() - 1; 

// this will give 18446744073709551615
cout << n - temp * s.length() - 1;

// reason because s.length() gives a unsigned number

• data types limits in c++

data	exact range	approx
short int	-32,768 to 32,767	-3E4 - 3E4
unsigned short int	0 to 65,535	0 - 6E4
unsigned int	0 to 4,294,967,295	0 - 4E9
int	-2,147,483,648 to 2,147,483,647	-2E9 - 2E9
long int	-2,147,483,648 to 2,147,483,647	-2E9 - 2E9
unsigned long int	0 to 4,294,967,295	0 - 4E9
long long int	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807	-9E18 - 9E18
unsigned long long int	0 to 18,446,744,073,709,551,615	0 - 1E19
signed char	-128 to 127	-1E2 - 1E2
unsigned char	0 to 255	0 - 2E2