-`std::ios_base::sync_with_stdio(false)`: by default, C++ works with C++ iostreams (like`std::cin`) and C style stdio streams (like`stdin`) by synchronizing them.

-`std::ios_base::sync_with_stdio(false)`: by default, C++ works with C++ iostreams (like`std::cin`, may not apply to new C++23`std::print`/`std::println`) and C style stdio streams (like`stdin`) by synchronizing them.

Since you should never need C style I/O (like`scanf`,`printf`), in C++, disabling this synchronization will make C++ I/O competitive with C style`scanf`.

-`std::cin.tie(0)`: By default, iostreams flush cout every time you read from cin, so that you will always display any output before reading any input.

You can disable this automatic flushing to make I/O faster. The exception is for interactive problems with interleaved inputs and outputs, for which you can either not use`cin.tie(0)` or flush explicitly with`cout.flush()`/`cout.endl`.

-`using namespace std;`: this saves lots of tedious typing of`std::` before all the standard library functions and objects. However, a blanket namespace import like this can cause name clashes, so don't name your variables or functions something common like`find` or anything from[this list](https://en.cppreference.com/w/cpp/symbol_index).

-`#include <bits/stdc++.h>`: this is a catch-all implementation-defined header in g++ that avoids having a list of dozens of includes like`#include <vector>`,`#include <iostream>`,`#include <string>`, etc. It should work on any CP judge site, but it is not a standard header.

-`#define int long long`: some people define`int` to always be (at least) 64-bit to avoid overflow issues, since most CP problems use numbers that fit in a 64-bit integer. However,be aware of unexpected issues:

-`#include <bits/stdc++.h>`: this is a catch-all implementation-defined header in g++ that avoids having a list of dozens of includes like`#include <vector>`,`#include <iostream>`,`#include <string>`, etc. It should work on any CP judge site, but it is not a standard header. On your local machine, it can be pre-compiled to greatly save compilation time.

-`#define int long long`: some people define`int` to always be (at least) 64-bit to avoid overflow issues, since most CP problems use numbers that fit in a 64-bit integer. However,this is**not recommended** because of many unexpected issues:

- C++ requires`main` to be a function returning`int` and not`long long`, so use`signed main` as a workaround.

- Function calls like`min(x, 0)` may complain that`0` is type`int`.

-May requiretwice as much memory than`int` and make the program slower, which may be important in extremely time-critical code.

-Requirestwice as much memory than`int` and may make the program slower, which may be important in extremely time-critical code.

- Otherwise you can use`typedef long long ll` or use the appropriate fixed-width integer types like`int64_t`.