Pre-Processor directive
# include <name of file> The Pre-Processor directives are not the part of C++ program. It is instruction to the compiler that we are going to include in the program. By this the compiler understand that the respective file is attached with the program. Example :- 1) # include <iostream> (This is a io stream directive , means that Input / Out put stream by this we can get the value from user and print i on the screen) 2) # include <cmath> (This is a c math directive , means that console math by this we can used the mathematical operators such as sqrtf etc.)