[C++] Chap 03 - Functions

Functions

• A function can have any finite number of arguments of varying data types / No function has more than one value returned (One or zero)
• Predefined functions : #import <cmath>, sqrt(x), pow(x, i), fabs(x), floor(x), ceil(x), round(x)

Random number generator

• rand() : takes no arguments, returns a uniform random integer btw 0 & RAND_MAX
• #includ <cstdlib>
• srand() : seed

Time

• #include <ctime>
• to return current time (elapsed in seconds since 1970.01.01) : time(NULL)

Components of Function Use

• Function declaration / Prototype
• Function Definition (implementation)
• Function Call

Function Declaration / Prototype

<rtn_type> FcnName(<formal-param-list>);
double totalCost(int num, double price);
// or
double totalCost(int, double);

• Designates the type of the “return val”, “name of func”, “number of arguments”, “type of formal parameters”
• Placed before any calls to the function (above the main)
• Formal parameter names are not needed : can only present data types of params.

Function definition

• Entire implementation of function is called function definition, lines inside the bracket is called function body.

• Can be placed after or before the main function.
• In case of before, function declaration can be omitted
• Can also be placed in a seperate file (another .cpp or for declaration, .h or .hpp)
• Functions are equal, no function is a ”part” of another.
• (formal) Parameters : Memory placeholders for data sent in

Function call

• Arguments at function call : actual arguments
• Function arguments can be literals, variables, expressions, or their combination

Simple example : multiple cpp files and header

Parameter vs Argument

• Often used interchangably but technically param is “formal” piece while argument is “actual”
• Formal (params/args) : in function declaration, header
• Actual (params/args) : in function call

Return statement

• return is optional statement for void function ( Closing bracket } implicitly return control from void function)
• Return type other than void MUST have return statement. (except for main())

Main

• Operating system calls main()
• should return int or void
• omitting return in main()is possible

Scope rules

• Local variables : declared inside the body of given function / available only within that func.
• Global variables : if declared outside function body
• Global constants : const double TAXRATE=0.05; Declared globally so all functions can use it.
• variables declared with const inside the function is also follows scope rules