Format of a C++ Program

We start here by presenting a simplistic view of the general format for C++ programs. This will help get you started programming. Later on, you will get into the object-oriented features of the language. For now though, here is the basic syntax you need to get going.


There are two forms of comment in C++.
  1. /* comment */
    A comment that carries over several lines begins with /* and ends with */

  2. // comment
    A comment on just one line - or part of a line - begins with //
    Typically, you'll see an inline comment at the end of a processing block such as } // end program
A comment block is simply a collection of comments contained by these characters: /*     */ The first lines of any C++ function should be a comment block. There can be many functions in a C++ program so a comment block is extremely helpful for yourself, or other programmers using your code. There are various conventions for the content of these comment blocks, but a block should minimally consist of:

Here is an example of a comment block that begins a simple program.

*  FileName:    ~ftp/pub/class/170/ftp/cpp/hello.cpp
*  Author:      Ada Lovelace
*  Purpose:
*               Demonstrate simple I/O by inputting a
*               name and outputting a welcome message.

include Statement

The first lines of the "main" function (which, for simple programs, is the only function) are:
#include <iostream>
using namespace std;
This statement informs the compiler of the location of the namespace where identifiers such as cout and endl (used in I/O) are located.

The #include <name> statement is referred to as a "preprocessor directive" because it instructs the C++ compiler where to find the necessary libraries before the compilation begins.

Function Header

The general format of a function header is return_type function_name (parameters). The simplest example of this is the function header for the main function. You'll see both forms of this header - either is acceptable. i.e.

C++ Statement

A statement is a C++ instruction that must end with a semi-colon ";" e.g. cout << "Hi There" << endl ;
Many C++ statements can be contained in one line, but there is no reason that you cannot spread the statement over several lines for readability - especially useful when you get to more complex output statements. Here is a trivial example:
	cout << "Hi"
	     << "There"
	     << endl;
Any line of text - e.g. cout, or an algebraic calculation - can be split over a number of lines to improve readability. As far as the compiler is concerned, the "statement" is officially concluded only when the semi-colon appears. Notice that in order to continue a literal string over more than one line, you need to end each line with a quotation mark.

Statement Block

The body of the function will contain a statement block which is a group of two or more statements enclosed in braces, begining with "{" and ending with "}"
You'll see these braces used to contain statement blocks all over C++ programs; wherever you want to group statements, such as in a IF statement. The following example shows just one big statement block in the main function.

Complete Program Example

*  FileName:    ~ftp/pub/class/170/ftp/cpp/hello.cpp
*  Author:      Ada Lovelace
*  Purpose:
*               Demonstrate simple I/O by inputting a
*               name and outputting a welcome message.

#include <iostream>	// preprocessor directive
using namespace std;	// necessary for I/O

void main() {    // statement block enclosed by {  and }

  string user_name;     // variable declaration

    cout << "Welcome to the world of C++" << endl;
    cout << "What is your name? ";
    cin >> user_name;
    cout << endl;
    cout << "Hi " 	// statement continued over several lines
	  << user_name 
          << "! Welcome to CS170." 
          << endl;

} // end main     <- comment used to clarify the "}"

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