C++ CH4 in funtion using c++ in all ab.ppt

Copyright © 2012 Pearson Education, Inc.
Chapter 4:
Functions

4.1
Modular Programming

Modular Programming
• Modular programming: breaking a program up
into smaller, manageable functions or modules
• Function: a collection of statements to perform a
task
• Motivation for modular programming:
– Improves maintainability of programs
– Simplifies the process of writing programs

4.2
Defining and Calling Functions

Defining and Calling Functions
• Function call: statement causes a function
to execute
• Function definition: statements that make
up a function

Function Definition
• Definition includes:
– return type: data type of the value that function
returns to the part of the program that called it
– name: name of the function. Function names follow
same rules as variables
– parameter list: variables containing values passed to
the function
– body: statements that perform the function’s task,
enclosed in {}

Function Definition
Note: The line that reads int main()is the
function header.

Function Return Type
• If a function returns a value, the type of the
value must be indicated:
int main()
• If a function does not return a value, its return
type is void:
void printHeading()
{
cout << "Monthly Salesn";
}

Calling a Function
• To call a function, use the function name
followed by () and ;
printHeading();
• When called, program executes the body of the
called function
• After the function terminates, execution resumes
in the calling function at point of call.

Functions in Program 4-1

Flow of Control in Program 4-1

Calling Functions
• main can call any number of functions
• Functions can call other functions
• Compiler must know the following about a
function before it is called:
– name
– return type
– number of parameters
– data type of each parameter

4.3
Function Prototypes

Function Prototypes
• Ways to notify the compiler about a function
before a call to the function:
– Place function definition before calling function’s
definition
– Use a function prototype (function declaration) – like
the function definition without the body
• Header: void printHeading()
• Prototype: void printHeading();

(Program Continues)

Program 4-5 (Continued)

Prototype Notes
• Place prototypes near top of program
• Program must include either prototype or full
function definition before any call to the
function – compiler error otherwise
• When using prototypes, can place function
definitions in any order in source file

4.4
Sending Data into a Function

Sending Data into a Function
• Can pass values into a function at time of call:
c = pow(a, b);
• Values passed to function are arguments
• Variables in a function that hold the values
passed as arguments are parameters

A Function with a Parameter
Variable
void displayValue(int num)
{
cout << "The value is " << num << endl;
}
The integer variable num is a parameter.
It accepts any integer value passed to the
function.

The function call in line 11 passes the value 5
as an argument to the function.

Other Parameter Terminology
• A parameter can also be called a formal
parameter or a formal argument
• An argument can also be called an actual
parameter or an actual argument

Parameters, Prototypes, and
Function Headers
• For each function argument,
– the prototype must include the data type of
each parameter inside its parentheses
– the header must include a declaration for
each parameter in its ()
void evenOrOdd(int); //prototype
void evenOrOdd(int num) //header
evenOrOdd(val); //call

Function Call Notes
• Value of argument is copied into parameter when
the function is called
• A parameter’s scope is the function which uses it
• Function can have multiple parameters
• There must be a data type listed in the prototype
() and an argument declaration in the function
header () for each parameter
• Arguments will be promoted/demoted as
necessary to match parameters

Passing Multiple Arguments
When calling a function and passing
multiple arguments:
– the number of arguments in the call must
match the prototype and definition
– the first argument will be used to initialize the
first parameter, the second argument to
initialize the second parameter, etc.

The function call in line 18 passes value1,
value2, and value3 as a arguments to the
function.

The return Statement
• Used to end execution of a function
• Can be placed anywhere in a function
– Statements that follow the return statement
will not be executed
• Can be used to prevent abnormal
termination of program
• In a void function without a return
statement, the function ends at its last }

Program 6-11(Continued)

4.5
Returning a Value From a
Function

Function
• A function can return a value back to the
statement that called the function.
• You've already seen the pow function,
which returns a value:
double x;
x = pow(2.0, 10.0);

Function
• In a value-returning function, the return
statement can be used to return a value from
function to the point of call. Example:
int sum(int num1, int num2)
{
double result;
result = num1 + num2;
return result;
}

A Value-Returning Function
{
double result;
result = num1 + num2;
return result;
}
Return Type
Value Being Returned

A Value-Returning Function
{
return num1 + num2;
}
Functions can return the values of
expressions, such as num1 + num2

The statement in line 17 calls the sum function,
passing value1 and value2 as arguments.
The return value is assigned to the total variable.

Another Example, from
Program 6-13

Function
• The prototype and the definition must
indicate the data type of return value
(not void)
• Calling function should use return value:
– assign it to a variable
– send it to cout
– use it in an expression

C++ CH4 in funtion using c++ in all ab.ppt

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