Before discussing the C++ language in detail, we summarize its conceptualfoundations. Since C++ consistently adheres to a small number of basicprinciples, acquiring a working understanding of these greatly hastens learningof C++ syntax.

Overview of program structure

The smallest unit of a C++ program is a token, which is a letteror symbol that the compiler can process. Appropriate groups of tokens yieldwords. Of these, identifiers (variable names) formatomic (single-element) expressions.Operators combine expressions to form new expressions.Terminating a valid expression with a semicolon yields astatement, which is equivalent to a sentence. Ablock, which is analogous to a paragraph, unifies andisolates one or more statements from the remainder of the program.Control structures determine the program flow according tothe outcome of logical operations, while functions and possiblysubroutines modularize compound statements by associating alabel with a frequently occurring sequence of statements. Finally,classes and objects structure relatedvariables and functions into generalized arrays. These, like a chapter, describea single topic, namely the properties of a related group of objects.

Tokens, names and keywords

The C++ compiler processes source-code lines in order of appearance and textwithin a line from left to right. A program is read as a sequence of tokensseparated by non-printing whitespace characters, which includetabs, carriage returns and spaces. Valid tokens are a–z, A–Z, 0–9 and certainpunctuation characters. Upper- and lower-case letters represent different tokenssuch that myVariable and myvariable are unrelated names. A word is a sequence oftokens terminated by whitespace. A reserved keyword is a wordsuch as int or if for which the complier has a specialinterpretation.