Programming :: Comprehending Umask And Mkdir In C++ - Create A Directory With Permissions 755

I'm having a bit of trouble understanding umask and mkdir in C++. In my program, I want to create a directory with the permissions 755.

If I do:-

Code:

The permissions come out all messed up.

But if I do:-

Code:

The permissions are set as expected.

I am having trouble understanding why umask(0); is needed, and what is the 'proper' way to use it so I can make my directory. From what I can understand from the man pages and everything, I need to set the umask in my program to allow it permission to make a directory with those permissions? And I don't get why umask(0); fixes it anyway!