• Text: messages intended for output or display
• Comments: messages which are visible to the programmer but do not affect the code (just describe it)
• C++ reserved words: these have special meanings whenever they appear outside strings and comments
• Identifiers: names you assign to things, such as
  • special sections of code (functions)
  • storage places for information (variables or constants)
  • specific types of data (e.g. integers, characters, etc)
  Identifiers can include letters, numbers, and underscores
• Library identifiers: identifiers appearing in pre-written sections of code that you can use in your own program

• syntax describes the rules which must be followed to make a legal statement in the language
• note that correct syntax does not necessarily imply a meaningful statement
• compilers check syntax while translating the program and reject illegal statements
• you can't write working programs without knowing the syntax, and you won't get fluent in the syntax without PRACTICE
• syntax rules can be described in words, by diagrams, or by grammar rules

1. Pre-processor directives: these give the compiler information about how to translate the source code (e.g. which libraries to include)
2. Constant definitions: which fixed values are used by the program (e.g. 1.196 in the metres-to-yards conversion)
3. Main program heading: indicates the start of the instructions to be executed
4. Main program declaration section: where the programmer defines variables (data storage spaces) to be used in the main program
5. Main program statement section: the actual instructions to be executed

Program parts (expanded)

1. Pre-processor directives:
   • information for the compiler, found at the start of the program
   • all start with the # symbol,
   • our most common use will be to include pre-written libraries of code, common ones include cstdio, cmath, cstdlib, cctype

     #include <cstdio>
     

2. Constant definitions:
   • name values which will be used repeatedly
   • make programs more readable and more maintainable
   • const <datatype> <identifier> = <value>;

     const int MinutesInDay = 1440;
     const float YardsInMetre = 1.196;
     

3. Main body heading:

   int main() {
   

4. Main body - declaration of variables
   • <datatype> <varname>;

     int   StartTime;        // Start time, integer value
     float CalculatedCost;   // Cost, floating point value
     char  UserInitial;      // Initial, a single character
     

5. Main body - statements section
   • series of statements (actions or instructions)
   • each ends with semi-colon ;
   • sometimes blocks of statements surrounded with curly brackets { }

        CalculatedCost = 17.6 * 9;
        UserInitial = 'M';
     

   Return a status value to the shell that controls user programs (0 is the default "everything is ok" status value):

      return 0;
   

   Finally, indicate the end of the main program section by matching main's opening bracket with a closing bracket:

    }
   

   ---

   A small example: Hello World

   // The most commonly written program in most languages
   
   
   #include <cstdio>
   
   int main()
   {
      printf("Hello World!");
      return 0;
   }
   

   If compiled and run, the output would look like:

   Hello World!
   

   Some notes on the Hello World code above:
   • cstdio contains the code for the printf routine
   • note the double-quotes around strings of output
   • statements end with the semi-colon ;
   • brackets must always match up (e.g. ( ) and { }

   ---

   Programming style: start good habits early!

   • Syntax rules still allow great freedom in the appearance of a program
   • Choose identifier names wisely, make them descriptive and to-the-point
   • You can include blank space (whitespace), either vertical or horizontal, where ever you like except in the middle of words/identifiers
   • Organised use of whitespace creates programs which are much easier to understand and modify
   • Comments: go from characters // to the end of the line, have no effect on the code (compiler ignores them) used to write explanations of the code for yourself and other programmers

   Examples of the effect of style:

   The two programs below take the radius of a circle, and calculate its area and diameter.

   They are functionally identical, but one would clearly be much easier to understand and modify than the other.

   POOR STYLE IS POOR PROGRAMMING - IT CAUSES ERRORS AND COSTS TIME AND RESOURCES IN THE REAL WORLD

   Poor use of whitespace

   #include                         <cstdio>
   const float 
                                    Pi
   =3.14                            ;int main() 
        { float
   radius; float                  diameter;float
                 circumference
   ;float area; printf( 
   "Enter radius\n"
         ;
                    scanf(
   "%f",
                   radius
                                       ); diameter=2
   *radius;circumference= diameter*
   Pi;area=Pi*radius*radius;printf("Radius %f diameter %f",
           radius , diameter 
   ); printf
                                       ("area %f\n"
   ,area);return
   0;} 
   

   Better use of whitespace

   #include  <cstdio>
   
   const float Pi = 3.14;
   
   int main() 
   { 
      float radius; 
      float diameter;
      float circumference;
      float area; 
   
      printf("Enter radius\n");
      scanf("%f", &radius);
   
      diameter = 2 * radius;
      circumference = diameter * Pi;
      area = Pi * radius * radius;
   
      printf("Radius %f diameter %f ", radius, diameter);
      printf("%f area %f\n", diameter, area);
      return 0;
   } 
   

   ---

   Another example: our metric conversion problem

   Design of a solution

   • 1. Read the fabric size in square metres
     • 1.1. Print prompt
     • 1.2. Read in the size
   • 2. Convert the fabric size to square yards
     • 2.1. size in square yards is 1.196 times size in square metres
   • 3. Display the fabric size in square yards

   The resulting source code

   #include <cstdio>
   
   using namespace std;
   // Conversion factor
   const float MetresToYards = 1.196;
   
   int main()
   {
      float SqMetres;  // input value
      float SqYards;   // converted value
   
      // Prompt and read input
      printf("Enter the fabric size in sq. metres\n");
      scanf("%f", &SqMetres);
   
      // Apply conversion factor
      SqYards = MetresToYards * SqMetres;
   
      // Display results
      printf("%f square metres equals %f square yards\n", SqMetres, SqYards);
   
      // finished
      return 0;
   }