C is the programming language in which (almost) the entire operating system Unix and most applications running on it are written.
C++ is an extension of C for object-oriented programming elements. It has the advantage of easy integration of vast amounts existing C code.
Various practical topics of C and C++ are described in some articles.
A quick reference for the C-professional are the List of standard C library functions and the List of POSIX library functions.
OpenCV (Open Computer Vision) is a powerful and comfortable environment for the implementation of a various projects in the field of image processing. The tutorial OpenCV practice: OCR for the electricity meter presents some aspects of OpenCV based on a practical application - the reading of an electricity meter.