A SAMPLE C++ PROGRAM:

   1.    /* This sample C++ program demonstrates basic program structure,
   2.       as well as console input and output.
   3.    */
   4.
   5.    #include <iostream>
   6.    using namespace std;
   7.
   8.    int main() {
   9.
   10.      cout << "\nThis program will find the quotient of two numbers\n"
   11.           << "that you enter.\n\n";
   12.   
   13.      double a,b;   // The two numbers entered by the user.
   14.        
   15.      cout << "Enter your first number:  ";
   16.      cin >> a;
   17.   
   18.      cout << "Enter your second number: ";   
   19.      cin >> b;
   20.   
   21.      if (b) {
   22.         double quotient = a/b;  // The quotient of the user's numbers;
   23.         cout << "The quotient is " << quotient << "\n\n";
   24.      }
   25.      else {
   26.         cerr << "Sorry.  Division by zero is not allowed.\n\n";
   27.      }
   28.   
   29.   } 


Commentary:

Line 1:   C++ uses the same types of comments as Java.  // starts a comment
          that ends at the end of the line.  /* starts a comment that ends
          with a */.  (This is NOT an example of a good comment for a real
          program!  It's just an example of a /* comment.)

Line 5:   Almost every C++ program uses header files.  To use a header
          file in a program, you have to #include it.  Standard header
          file names are enclosed between < and >.  The iostream standard
          header file defines cin, cout, and cerr (among other things).  These
          are objects that are used for standard console-style I/O.  As 
          another example, the standard mathematical functions are defined
          in a header file named cmath.  If you want to use them, you should
          "#include <cmath>" at the beginning of the program.  The functions
          declared in this header file include things like sin(x), abs(x),
          sqrt(x), and pow(x,y).  (In Java, the same functions are static
          members of the Math class and have names such as Math.sin and
          Math.sqrt.  In C++, they are not members of a class, but you
          have to include the cmath header if you want to use them.)

Line 6:   This line (or something equivalent) is required by the C++
          standard, but it is NOT required by the compiler that we will
          be using.  According to the standard, the proper names for
          standard identifiers such as cout and sqrt are std::cout and
          std::sqrt.  The directive "using namespace std;"  makes it
          possible to use these identifiers without the "std::" prefix.

Line 8:   A C++ program must have a main() function.  (All subroutines in
          C++ are called "functions", whether or not they return a value.)
          This function cannot be a member of a class.  It should be declared
          as "int main()" or as "int main(int argc, char* argv[])".  In the
          second form, argv is an array of command-line parameters, and
          argc is the number of items in the array.  A return value of 0
          from main() tells the operating system that the program
          "succeeded", while any non-zero value indicates "failure".  If no
          return statement is included, as in this example, then a return
          value of 0 is provided automatically.
      
Line 10:  Output to the console is done with the console output object,
          cout.  The << operator is used with cout to specify the output.
          Note that you can string together several output items by using
          several << operators.  A \n in a string indicates a new line.
          
Line 13:  Simple variable declarations are similar in C++ and Java.  The
          most common types in C++ are int, double, bool, and char.
          Note that the true/false type is named "bool" rather than
          "boolean".  The char type represents 8-bit ASCII characters,
          not 16-bit Unicode characters as in Java.

Line 16:  Input from the console is done with the console input object,
          cin.  The >> operator is used to put an input value into a variable.
          You can string together several input operations, as in
          "cin >> a >> b;".  Note that the direction of the arrows indicates
          the direction of the flow of information:  In "cout << a", a value
          is being sent from a to cout.  In "cin >> a", a value is being sent
          from cin into the variable a.

Line 21:  Control structures (if, while, do, for, switch) are almost identical
          in C++ and Java.  One significant difference is that in C++, a
          numerical value can be used wherever a Boolean value would
          ordinarily be used.  A numerical value of zero is considered to
          be false; any non-zero value is considered to be true.  Thus,
          in this sample program, "if (b)" is testing whether b is non-zero.
          It might be clearer to say "if (b != 0)", but the effect is 
          the same.
          
Line 22:  Just as in Java, a variable can be defined inside a block.  The
          variable is then local to that block.

Line 26:  There is an object called cerr which is supposed to be used
          for output about errors that occur when the program is running.
          Error output might be sent to a different location than the output
          from cout, such as to an error log file.  In practice, cerr is
          mostly used in non-interactive programs, and you will rarely
          encounter it.