What is preprocessor directives, main function, expression and declaration?

Preprocessor directives has #include to specify that its a preprocessor directive, #include “myfile.h” represents a library being called “myfile.h” to be preprocessed before the compiler starts. The main function is the building bocks of every .cpp file. The main code goes in here, etc: function calling. The expression statements are input and output stream going to the terminal or retrieving from the terminal. The declaration statements include using variables in operations that produce a result.

The preprocessor directive tells the computer to use a specific library of code. The main function is the initial process containing our expression and declarations in the code. The expression statement is the output we want the program to give us and the declaration statement is the variables that we set in the program. The return statement creates an end to the program or allows it to loop after processing.

The preprocessor directive directs the compiler to include/import/copy a predefined/prewritten code from the library into our code before compiling our code.

An expression statement is what we use to output/input to and from the console/terminal.
A declaration statement is simply where we declare a fact of our program like a variable.
Main function is where the compiler starts our program execution. Without the main function, a program will not run.