parameter variables are one kind of variable;

double disk_area(double radius)

another kind of variable declaration: a NAMED CONSTANT

const 

= expression	ASSIGNMENT to that expression

for a declaration statement that declares a named constant:

const <type> <DESIRED_NAME> = <expression> ;

const double PI = 3.14159;

const int TSPS_PER_TBL = 3;

130 STYLE STANDARD: NO MAGIC NUMBERS (no "bare" literals)

130 STYLE STANDARD: named constants are to be written in all-uppercase

180 + (.04 * attendees(ticket_price))

FIXED_SHOW_COST + (PER_ATTENDEE_COST * attendees(ticket_price))

* named constants CAN make code easier to read
* named constants CAN make code easier to MAINTAIN and CHANGE

Where can these declarations go?

* in the header (.h) file: that's where funct_play2 puts them;
* inside the function body;

SCOPE

IN LECTURE EXERCISE:

1. write a reasonable named constant declaration for the fixed cost of
   a performance of $180

2. write a reasonable named constant declaration for the cost per
   attendee of 4 cents

3. write a reasonable named constant declaration for the base
   attendance when the ticket price is $5 (that is, for 120)

4. write a reasonable named constant declaration for the base
   ticket price of $5

 

ONLY RESPONSIBLE for SECTIONS 1- 3 in HTDP packet for Exam #1

----- this is material now for Exam 2!

there are 4 basic structures in programming! (some will say 3...)

sequence: statements that are one after the other are done one
              after the other;

procedure: when you call a function, you know it will come back

Today, we're setting up for the 3rd basic structure:
BRANCHING

(later: after section 5 --- we'll have the 4th basic structure:
REPETITION)

STEP ONE: BOOLEANS and RELATIONS

bool    true false

1 is an example of an int literal
2.0 is an example of a double literal
true is an example of a bool literal


logical expressions
boolean expressions

and, relational expressions

Start with relational expressions:

relational operators:

<	   3 < 8
>
<=         3 <= 8 is true,
	   3 <= 2 is false,
           3 <= 3 is true
>=
==         see if two things are EQUAL!!!!!


3 == 3

!= not equal

4 != 3

 (a + b - c) == (d - a)


IN CLASS EXERCISE #5

5. write a relational expression that is true if a parameter variable
   age is less than or equal to 12

can write functions that return a boolean!

is_child

// contract: is_child: int -> bool

bool is_child(int age)

// purpose: if a person's <age> is 12 or less, return true, else
//          return false.
//
// examples: is_child(11) should return true
//           is_child(12) should return true
//           is_child(13) should return false

bool is_child(int age)
{
    const int CHILD_LIMIT = 12;

    return (age <= CHILD_LIMIT);
}

consider:		70 <= grade <= 100
WON'T WORK in C++!
     70 <= grade is true or false,
     then true or false is compared to <= 100...!

Need:   70 <= grade 
        and 
        grade <= 100

I need BOOLEAN operators:

and, or, not
&&   ||  !

(70 <= grade) && (grade <= 100)

(and drew TRUTH TABLES for and, or, not on the chalkboard!)