chapter 6 - functions Flashcards
(43 cards)
1
Q
modular programming
A
- breaking a program up into smaller, manageable functions or modules
2
Q
function
A
- a collection of statements to perform a task
- statements that make up a function
- can have multiple parameters
- an argument declaration must be listed in the function header ( ) for each parameter
3
Q
motivation for modular programming
A
- improves maintainability of programs
- simplifies the process of writing programs
4
Q
function call
A
statement causes a function to execute
5
Q
function definition includes:
A
- 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 variable
- parameter list: variables containing values passed to the function
- body: statements that perform the functions task, enclosed in { }
6
Q
function format
A
int main () {
cout «_space;“Hello World\n; // function
return 0; // body
}
int = return type
main = function name
( ) = parameter list
7
Q
function return type
A
- if a function returns a value, the type of the value must be indicated
- if a function does not return a value, its return type is void
8
Q
calling a function
A
- main can call any number of functions
- functions can call other functions
- value of argument is copied into parameter when the function is called
- a parameter’s scope is the function which uses it
9
Q
function prototypes
A
- place function definition before calling function’s definition
- place prototypes near top of program
- program must include either prototype or full function definition before any call to the function
- when using prototypes, can place function definitions is any order in source file
- there must be a data type listed in the prototype ( )
10
Q
how calling a function works
A
- when called, program executes the body of the called function
- after the function terminates, execution resumes in the calling function at point of call
11
Q
what must the compiler know about a function
A
- compiler must know the following about a function before it is called
- name, return type, number of parameters, data type of each parameter
12
Q
sending data into a function
A
- can pass values into a function at time of call
- values passed to functions are arguments
- variables in a function that hold the values passed as arguments are parameters
13
Q
other parameter terminology
A
- 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
14
Q
function call format
A
evenOrOdd (int);
15
Q
function prototype format
A
int evenOrOdd (int);
16
Q
function header format
A
int evenOrOdd (int num)
17
Q
when passing multiple arguments . . .
A
- 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, n argument to initialize the n parameter
18
Q
pass by value
A
- when an argument is passed to a function, its value is copied into the parameter
- changes to the parameter in the function does not affect the value of the argument
19
Q
functions can be used to . . .
A
- implement user choices from menu
- implement general-purpose tasks:
20
Q
higher-level functions
A
- can call general-purpose functions, minimizing the total number of functions and speeding program dev. time
21
Q
return statement
A
- 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 }
22
Q
value-returning function
A
- a function can return a value or an expression back to the statement that called the function
- return statement can be used to return a value or expression from function to the point of call
23
Q
value-returning function format
A
double sum (double num1, double num2) {
int result = num1 + num2;
return result;
} // or return num1 + num 2;
where total = sum( value1, value2);
double sum = return type
result = value being returned
24
Q
different return value methods
A
- assign it to a variable
- send it to cout
- use it in an expression
25
returning a boolean value
- function can return true or false
- declare return type in function prototype and heading as bool
- function body must contain return statement(s) that return true or false
- calling function can use return value in a relational expression
26
local variable
- variables defined inside a function are local to that function. they are hidden from the statements in other functions, which normally cannot access them.
- other functions may have separate, distinct variables with the same name
- not automatically initialized. must be initialized by programmer
27
local variable lifetime
- a function's local variables exist only while the function is executing
28
how does local variable lifetime work in a function
- when the function begins, its local variables and its parameter variables are created in memory
- when the function ends, the local variables and parameter variables are destroyed
- any value stored in a local variable is lost between calls to the function in which the variable is declared
29
global variable
- any variable defined outside all the functions in a program
- can be accessed by all functions that are defined after the global variable is defined
- should be avoided because they make programs difficult to debug
- any global variable created should be global constants
- global variables are automatically initialized to 0 (numeric) or NULL (character) when the variable is defined
30
global variable scope
- the portion of the program from the variable definition to the end
31
static local variables
- unlike local variables, static local variables retain their contents between function calls
- are defined and initialized only the first time the function is executed. 0 is the default initialization value
32
default argument
- an argument that is passed automatically to a parameter if the argument is missing on the function call
- must be a constant declared in prototype:
void evenOrOdd (int = 0);
- can be declared in header if no prototype
- multi-parameter functions may have default arguments for some or all of them
int getSum (int, int = 0, int = 0);
33
default argument rules/format
- if not all parameters to a function have default values, the defaultless ones are declared first in the parameter list
int getSum (int, int = 0, int = 0); // OK
int getSum (int, int = 0, int) ; // WRONG
- when an argument is omitted from a function call, all arguments after it must also be omitted
sum = getSum (num1, num2); // OK
sum = getSum (num1, , num3); // WRONG
34
reference variables as parameters
- a mechanism that allows a function to work with the original argument from the function call, not a copy of the argument
- allows function to modify values stored in the calling environment
- provides a way for the function to 'return' more than one value
35
reference variable
- an alias for another variable
- defined with an ampersand (&)
- changes to a reference variables are made to the variable it refers to
- use reference variables to implement passing parameters by reference
36
reference variable format
void getDimensions (int&, int&);
- each reference parameter must contain &
- space between type and & is unimportant
- must use & in both prototype and header
37
reference variable rules
1. argument passed to reference parameter must be a variable - cannot be an expression or constant
2. use when appropriate - don't use when argument should not be changed by function, or if function needs to return only 1 value
38
overloading functions
- have the same name but different parameter lists
- can be used to create functions that perform the same task but take different parameter types or different number of parameters
- compiler will determine which version of function to call by arguments and parameter lists
39
exit ( ) function
- terminates the execution of a program
- can be called from any function
- can pass an int value to operating system to indicate status of program termination
- usually used for abnormal termination of program
- requires cstdlib header file
40
exit function format
- exit (0);
- cstdlib header defines two constants that are commonly passed, to indicate success or failure:
exit (EXIT_SUCCESS);
exit (EXIT_FAILURE);
41
stub
- a dummy function used in place of an actual function
- usually displays a message indicating it was called. may also display parameters
42
driver
- a function that tests another function by calling it
- various arguments are passed and return values are tested
43
stubs and drivers are useful for . . .
- useful for testing and debugging program and function logic and design
