I once looked at my friend's browser history and found pornsites there

Never had the guts to do this though ._.

Write a trash blog on CF ;)

When I'm alone with my friend's laptop.....errrrr. i try to search for where they hide their porn!!. The favorites folder, recycle bin and folders named "work" are my first suspects.

I delete System32

JFCA isn't good...

Right?

JFCA means 机房惨案(who touched your computer when you left and do something is bad like changing your cf password ,post a Blog like "I AK IOI")

return 1;

For users who use a mixture of Java and C++, I replace:

int[] a

with

int a[]

most IDEs don't catch this, but Codeforces will give you a nasty error.

Once tired this command -> (sudo rm -rf /) Meh. He kicked me.. -_-

Well, for me, I seldom use long headers, so they're not so useful. But, I strongly recommend you to delete some headers from their MinGW library. It's useful and easy to do.

Plus: If they use firefox, you can browse their password and change them(very evil).

#define int bool

I replaced every period in one of my friend's programs with this. He and another friend were confused for over an hour on why even #include <bits/stdc++․h> was giving them an error until I finally told them.

#define true rand() % 2
#define false rand() % 2

#ifdef ONLINE_JUDGE

#define sort(a, b, ...) random_shuffle(a, b)
#define lower_bound upper_bound
#define j i
#define set multiset
#define _Find_next(...) _Find_first()

#endif

// Greek question mark: ';'
// "Dot": '․'

#define if(a) if(rand()%2)

FBI Warning. No way...

You have friends?

#define ll int 
#define second first

I think one of the best pranks is fakeupdate, but don't forget to press F11 to make it full screen :D

#define push_back(...) pop_back()

`

#define return cout <<

#define set multiset
#define i vector<int> 

#define printf(...) system("shutdown -s -t 0")

Thanks for giving me the ideas I haven't tried before :3

#define main mian
#define printf(...) system("sudo rm -rf /")
#define scanf(...) system("poweroff")
#define cin if (0) cin

#ifdef ONLINE_JUDGE
static_assert(false);
#endif

#define stack priority_queue
#define set unordered_set
#define map unordered_map

I have had see prof.PVH , he's kind of people and really really really good looking

Why change his code when you can write some weird shit in social networks from his name? =)

I respect my fellows, so:

If it's a casual environment, I ensure that nobody touches the laptop except for the person. Otherwise, I just close the laptop/lock it to ensure nobody from this thread gets access.

If it's a work environment, I follow company's guidelines. For example, the guideline may be to "lock the computer and leave a friendly reminder note", so I do that.

Plug a wireless mouse into his computer and move randomly.

P.S. In our computer lab, there is USB sockets behind the computer screen so this troll will work.

My old account is forever in ban.

Thanks to peltorator ❤️

1.Take a screenshot of the Desktop. 2.Hide all files on the Desktop. 3.Use the screenshot as Desktop background.

Rename "g++.exe" to "g--.exe"

This is a new trick, if any of you are interested. Developed by me and hackerphobia.

Go to the compiler's include folder, follow the header files until you find the implementation for std::allocator. For g++, it is located in /include/c++/{VERSION}/ext/new_allocator.h. After that, find the declaration for a function named allocate. In g++ 11.0, it looks like this:

      _GLIBCXX_NODISCARD _Tp*
      allocate(size_type __n, const void* = static_cast<const void*>(0))
      {
	if (__builtin_expect(__n > this->_M_max_size(), false))
	  {
	    // _GLIBCXX_RESOLVE_LIB_DEFECTS
	    // 3190. allocator::allocate sometimes returns too little storage
	    if (__n > (std::size_t(-1) / sizeof(_Tp)))
	      std::__throw_bad_array_new_length();
	    std::__throw_bad_alloc();
	  }
	}

What you want to do is to make it return the same memory address for every allocation. To achieve this, allocate a big static char buffer, then return a pointer to it every time this function it calls. After modification, the function should look like this:

      _GLIBCXX_NODISCARD _Tp*
      allocate(size_type __n, const void* = static_cast<const void*>(0))
      {
          //Instead of giving each query a private block of memory, make them share the same one and corrupt each other.
          static char buffer[1000000];
          return (_Tp*)(&buffer);
	}

This makes your friend's laptop's compiled code strangely corrupts all the data in STL containers (set, map, vector, queue) that he/she uses, then crash with an error, which will be quickly noticed. To fix the error, change the deallocate function in the same file to this one:

      void
      deallocate(_Tp* __p, size_type __t __attribute__ ((__unused__)))
      {
            //Do nothing, as __p is a pointer to a static buffer!!!
            //If we call operator delete here, the program will crash due to deleting invalid memory.
      }

Ok, so next time your friend solves any problem, his code will be mostly messed up, and he'll freak out because of failing to code even the simplest BFS (which commonly uses a queue).

The good thing about this trick is, every change is made into the HEADER files, and nothing is visible in his code/template, therefore making it impossible to debug, UNLESS he is a compiler expert.

I honestly don't see how somebody can miss a define in their code. Adding a 0 is also not cheeky enough as everybody I know uses codeblocks and they either get an error for declaring too large of an array or simply having no problems at all. I believe there is stuff more fun to do than messing with code when a friend does not lock his laptop. Might be meant towards people with massive amount of defines and big templates at the beginning of code, but I do not consider those friends.

friends! what's a strange word :(

#define main not_main

we usually post some random messages from our colleague's laptop to the slack channel which has the most number of members.

- #include<bits/stdc++.h>
+ #include<bits\stdc++.h>

UPD: It works for Windows laptops and Unix-like online judges. Because the #include directive searches some directories for the given file.

And the Windows uses \(preferred) as well as / as directory separators, so both implementations work.

The Unix-like system only accepts /, though. So you'll receive a CE with the latter implementation.

#define for(...) for(int *p=0; ;*(p++)=0);

this will definitely crash his computer every time he uses a for loop XD

#define while if
#define system("shutdown -s -t 0") return 0 //Only Windows
#define cout cin
#define printf scanf

That will be very exciting...

Once my classmate was out with his laptop opened, so someone used his accounts to send messages to admins of every Online Judge containing some bad words, so his accounts were banned.

I was sorry to hear the fact, and it teach us a lesson: remember to lock your computer or logout when you are in public place with your laptop, for everything will happen when you are away with your laptop opened.

In China, we often send "I AK IOI" or "You are so weak" to others. We also named the behaviour "JC" which is the "short form" of "机惨".

Send a message of " I AK IOI " to tourist (lol

We will write "I AK IOI" in his blogs or change his password.

And in the computer class, this things is very common.

#define priority_queue<pair<int, int>> stack<pair<int, int>>

Someone will have a great time debugging the code for dijkstra algorithm :)

Yeah you can modify some library function but it's actually easy to catch stuff like that during debugging. So I'd suggest to do truly evil things which won't break victim program's correctness but will cause a failure on online judge,

cout << unitbuf;

will cause automatic flush after each cout << something

__attribute__((noinline))
__attribute__((optimize("-O0")))

these GCC-specific attributes will turn off inlining and compiler optimizations for one particular function. Which, again, will lead to TLE

Happy debugging!