Hello everyone! Today I want to write about common C++ mistakes that may seem correct while writing code, but are actually wrong upon deeper inspection. If you have any suggestions, I can add them to this blog.

size_t type is unsigned

When you get the size of some container it returns unsigned integer, not regular integer. It may lead to mistakes like this:

for (int i = 0; i < Ar.size() - 3; i++)

If size of Ar is less than 3, Ar.size() - 3 won't be some negative integer, it will be large positive integer because of how unsigned integers work.

Common mistake with pointers

Let's say you wanted to create a vector of multiple pointers, and you wrote it like this:

vector<node*> T(N, new node());

This might seem correct but it isn't. Keep in mind that all those pointers will point into one node, not N nodes, so if you change one, it will affect all of them. Instead, you have to add them one by one:

vector<node*> T;
for (int i = 0; i < N; i++) T.push_back(new node());