Erle Robotics C++ GitBook

Line-By-Line Explanation

• // indicates that everything following it until the end of the line is a comment: it is ignored by the compiler. Another way to write a comment is to put it between /* and */ (e.g. x = 1 + /sneaky comment here/ 1;). A comment of this form may span multiple lines. Comments exist to explain non-obvious things going on in the code.

• Lines beginning with # are preprocessor commands, which usually change what code is actually being compiled. #include tells the preprocessor to dump in the contents of another file, for example #include <stdio.h>.

• int main() {...} defines the code that should execute when the program starts up. The curly braces represent grouping of multiple commands into a block.

• cout << : This is the syntax for outputting some piece of text to the screen.

• Namespaces: In C++, identifiers can be defined within a context – sort of a directory of names – called a namespace. When we want to access an identifier defined in a namespace, we tell the compiler to look for it in that namespace using the scope resolution operator (::). Here, we’re telling the compiler to look for cout in the std namespace, in which many standard C++ identifiers are defined. A cleaner alternative is to add the following line below line 2:

  using namespace std ;
  

This line tells the compiler that it should look in the std namespace for any identifier we haven’t defined. If we do this, we can omit the std:: prefix when writing cout. This is the recommended practice.

• Strings: A sequence of characters such as Hello, world is known as a string. A string that is specified explicitly in a program is a string literal.

• Escape sequences: The \n indicates a newline character. It is an example of an escape sequence – a symbol used to represent a special character in a text literal. Here are all the C++ escape sequences which you can include in strings:

• return 0 indicates that the program should tell the operating system it has completed successfully. This syntax will be explained in the context of functions; for now, just include it as the last line in the main block.

Note that every statement ends with a semicolon (except preprocessor commands and blocks using {}).