• Announce
  • Quiz Wednesday
  • Continue to Read Chapter 3

• More About Syntax
  • need a precise notation
  • more formal method

• Syntax Rules

  1. <identifier> -> //a sequence of letters and/or digits that begin with a letter//

  2. <expression> -> <str expression>

  3. <expression> -> <int expression>

  4. <str expression> -> <identifier>

  5. <str expression> -> "//any string of printable chars//"

  6. <str expression> -> <str expression> + <str expression>

  7. <int expression> -> //any sequence of digits//

  8. <int expression> -> <identifier>

  9. <int expression> -> <int expression> <int op> <int expression>

  10. <int op> -> + | - | * | / | %

  11. <statement> -> <identifier> = <expression>;

  12. <compound statement>	->	{
      		//a sequence of <statements>s//
      		}

• To Use: substitute, multiple times as necessary:

• Statement Example
  Want: pigLatin = tail + firstL + "ay";

 EXAMPLE:
<statement> -> <identifier> = <expression>;
<statement> -> pigLatin = <expression>;
<statement> -> pigLatin = <str expression>;
<statement> -> pigLatin = <str expression> + <str expression>;
<statement> -> pigLatin = <identifier> + <str expression>;
<statement> -> pigLatin = tail + <str expression>;
<statement> -> pigLatin = tail + <str expression> + <str expression>;
<statement> -> pigLatin = tail + <identifier> + <str expression>;
<statement> -> pigLatin = tail + firstL + <str expression>;
<statement> -> pigLatin = tail + firstL + "ay";

• Example involving compound statement:
  (assuming result5 is an int variable)

  {

  s = "Hello!";

  k = result5;

  }

  
  

  #12	<compound statement>	->	{
  			<statement>
  			<statement>
  			}
  	<compound statement>	->	{
  #11			<identifier>=<expression>;
  #11			<identifier>=<expression>;
  			}
  	<compound statement>	->	{
  #1			s=<expression>;
  #1			k=<expression>;
  			}
  	<compound statement>	->	{
  #2			s=<str expression>;
  #3			k=<int expression>;
  			}
  	<compound statement>	->	{
  #5			s="Hello!";
  #8			k=<identifier>;
  			}
  	<compound statement>	->	{
  			s="Hello!";
  #8			k=results;
  			}

• What about IF-ELSE or IF?
  

  13.	<statement>	->	if (<boolean expression>)
  			<compound statement>
  			else
  			<compound statement>

  
  
  

  14.	<statement>	->	if (<boolean expression>)
  			<compound statement>

• Leave Syntax Study for Now
  
  
  
  

• Loops!! ... and it all happened again ...
  
  
  
  

• The while Loop
  
  

  while (boolean expression)

  {

  statement;

  ...

  statement;

  }



  • statements repeated as long as logical expression is true
  • For proper loop: at least one of previous statements must cause change in logical expression

• Looping Examples