C++ Part 41

Review Part IV

Function Call
A function call is an expression consisting of the function name followed
by arguments enclosed in parentheses. If there is more than one argument,
the arguments are separated by commas. A function call is an expression
that can be used like any other expression of the type specified for the
value returned by the function.
SYNTAX
Function_Name(Argument_List)
where the Argument_List is a comma-separated list of arguments:
Argument_1, Argument_2, . . . , Argument_Last
EXAMPLES
side = sqrt(area);
cout << "2.5 to the power 3.0 is " << pow(2.5, 3.0);

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A Function to Convert from int to double
The notation static_cast can be used as a predefined function
and will convert a value of some other type to a value of type double. For
example, static_cast(2) returns 2.0. This is called type casting.
(Type casting can be done with types other than double, but until later in
this book, we will do type casting only with the type double.)
SYNTAX
static_cast(Expression_of_Type_int)
EXAMPLE
int total_pot, number_of_winners;
double your_winnings;
. . .
your_winnings =
static_cast(total_pot)/number_of_winners;

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Function Declaration
A function declaration tells you all you need to know to write a call to the
function. A function declaration is required to appear in your code prior to
a call to a function whose definition has not yet appeared. Function
declarations are normally placed before the main part of your program.
SYNTAX
Type_Returned Function_Name(Parameter_List);
Function_Declaration_Comment
where the Parameter_List is a comma-separated list of parameters:
Type_1 Formal_Parameter_1, Type_2 Formal_Parameter_2,...
..., Type_Last Formal_Parameter_Last
Example
double total_weight(int number, double weight_of_one);
//Returns the total weight of number items that
//each weigh weight_of_one.

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A Function Is Like a Small Program
To understand functions, keep the following three points in mind:
■ A function definition is like a small program and calling the function is the
same thing as running this “small program.”
■ A function uses formal parameters, rather than cin, for input. The arguments to
the function are the input and they are plugged in for the formal parameters.
■ A function (of the kind discussed in this chapter) does not normally send any output
to the screen, but it does send a kind of “output” back to the program. The
function returns a value, which is like the “output” for the function. The function
uses a return statement instead of a cout statement for this “output.”

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Procedural Abstraction
When applied to a function definition, the principle of procedural
abstraction means that your function should be written so that it can be
used like a black box. This means that the programmer who uses the
function should not need to look at the body of the function definition to
see how the function works. The function declaration and the accompanying
comment should be all the programmer needs to know in order to use
the function. To ensure that your function definitions have this important
property, you should strictly adhere to the following rules:
HOW TO WRITE A BLACK-BOX FUNCTION DEFINITION (THAT RETURNS
A VALUE)
■ The function declaration comment should tell the programmer any and all conditions
that are required of the arguments to the function and should describe
the value that is returned by the function when called with these arguments.
■ All variables used in the function body should be declared in the function body.
(The formal parameters do not need to be declared, because they are listed in
the function declaration.)

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Make a Loop Body a Function Call
Whenever you have a loop nested within a loop, or any other complex
computation included in a loop body, make the loop body a function call.
This way you can separate the design of the loop body from the design of
the rest of the program. This divides your programming task into two
smaller subtasks.

C++ Part 38

Review Part I
Identifiers
Identifiers are used as names for variables and other items in a C++
program. An identifier must start with either a letter or the underscore
symbol, and the remaining characters must all be letters, digits, or the
underscore symbol.

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Variable Declarations
All variables must be declared before they are used. The syntax for variable
declarations is as follows:
SYNTAX Type_Name Variable_Name_1, Variable_Name_2, . . .;
EXAMPLES:
int count, number_of_dragons, number_of_trolls;
double distance;

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Syntax
The syntax for a programming language (or any other kind of language) is
the set of grammar rules for that language. For example, when we talk
about the syntax for a variable declaration (as in the box labeled “Variable
Declarations”), we are talking about the rules for writing down a well-formed
variable declaration. If you follow all the syntax rules for C++, then
the compiler will accept your program. Of course, this only guarantees that
what you write is legal. It guarantees that your program will do something,
but it does not guarantee that your program will do what you want it to do.

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Assignment Statements
In an assignment statement, first the expression on the right-hand side of
the equal sign is evaluated, and then the variable on the left-hand side of
the equal sign is set equal to this value.
SYNTAX Variable = Expression;
EXAMPLES distance = rate * time;
count = count + 2;

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Initializing Variables in Declarations
You can initialize a variable (that is, give it a value) at the time that you
declare the variable.
SYNTAX
Type_Name Variable_Name_1 = Expression_ for_Value_1,
Variable_Name_2 = Expresssion_ for_Value_2, . . .;
EXAMPLES
int count = 0, limit = 10, fudge_factor = 2;
double distance = 999.99;
Alternative Syntax for Initializing in Declarations
Type_Name Variable_Name_1 (Expression_ for_Value_1),
Variable_Name_2 (Expression_ for_Value_2), . . .;