Preprocessor Directives that are home to iostreams, tell the compiler to bring in header files(files that already have prestored code inside them) into the programs for the programmer to use.
The main function (int main) is the function that the program will run first out of all the other functions as the program will run everything inside the main function bracket.
The expression statements that are inputted by the programmer are commands to the programs that will be run by the program after it is finished compiling.
Declaration statements are statements that give out instructions that determines a set of data in a program.
Return statements (or in this cast return 0) terminates the program. In other functions returns statements return a value to the main functions.