CSCI 161: Introduction to Programming Function

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

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

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

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

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

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);

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)

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

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

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

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);

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);

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);

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();

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

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 {}

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

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

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.

(Program Continues)