1. CSCI 161: Introduction to Programming Function

2. 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

3. Functions
Function - set of statements collected together and given a name
Allow programmer to signify entire set of operations with single name
Make programs shorter and simpler
May include the computation of a value

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

5. Function Call e.g. f(x, y); Call
act of executing statements associated with function
done by writing name of function, followed by list of expressions enclosed in parenthesis
arguments - allow passage of information to function
function call is simply an expression

6. Function Return e.g. z = f(x, y); Return
once function completes, returns to program step where call was made and continues
may also send back results to calling program
returning a value

7. math library #include <cmath>
functions that take value of type double as argument and return value of type double
sqrt, exp, log, sin, cos
e.g.
root = sqrt(3.0);
distance = sqrt(x*x + y*y);
tangent = sin(x) / cos(x);

8. Function Prototype(Declarations)
name of the function
type of each argument and descriptive names
type of value that function returns
Has form
result-type name(argument-specifiers);
where
result-type – data type of function result
name – name of function itself
argument-specifiers – argument data types (optionally followed by descriptive names)

9. More on Prototypes e.g. double sqrt(double);
Function sqrt takes one argument of type double and returns a value of type double
e.g. double sin(double radians);
Name for argument provides further information for programmer using function

10. void data type
Keyword void is used to indicate no arguments or no return value
e.g.
int getNumber(void);
void menu(void);

11. Writing Your Own Functions
Two distinct steps
1. Specify function prototype (after the includes, before main) - shows format
2. Provide implementation of function (actual steps involved) - shows details

12. Function Body Block consisting of statement in { } Similar to main
May include variable declarations
Return statement - required if function returns a result back to caller
return (expression);

13. Celsius to Fahrenheit Prototype double CtoF(double c); Implementation{
return (9.0/5.0 * c + 32); }
Another implementation
double f;
f = (9.0/5.0 * c + 32);
return (f);

14. Main Program for CtoF To call function, could use
f_value = CtoF(30.0);
cout << f_value;
Or simply use
cout << CtoF(30.0); or
double c_value = 30.0;
f_value = CtoF(c_value);

15. 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();

16. 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

17. 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 {}

18. 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

19. 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

20. Example
output if each entered value is even or not, terminate when the number entered is -1
Done in class

21. 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

22. 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.

23. (Program Continues)