show_functions

show_functions - CHAPTER 5 Programming with Functions...

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Unformatted text preview: CHAPTER 5 Programming with Functions March 28, 2008 Motivation Why Functions? ◮ Provides re-usability of common or often used algorithms (such as prompting a user for input). ◮ Let’s you maintain “algorithm focus” — don’t clutter up any function (specifically main() ) with “little bits of logic” that aren’t intrinsic to the task at hand. ◮ Allows you to provide a single, explicit interface to data or algorithms specific to your application. For instance, an interface for calculating specialized equations, access to a laboratory device, or access to a database of collected data, . . . Motivation f ( x ) ∼ double f( double x ) ◮ Conceptual idea similar to the f ( x ) you know. ◮ Functional composition: f ( sin ( y ) , cos ( y )) ◮ Recursion: a n = a n- 2 + a n- 1 . Function Anatomy Types of Functions User-Defined Function A function you have written. Library Function Function you use but didn’t write. Library functions come in many different forms: commercial libraries, FOSS libraries, system libraries, your partner’s library. main() is a user-defined function provided for every application. Function Anatomy Parts of a Function 1 / ** 2 * Main f u n c t i o n comment d e s c r i b e s what t h e f u n c t i o n does , s p e c i a l p r o p e r t i e s 3 * o f i t s arguments , what i t r e t u r n s , and i t s r e t u r n i n t e r p r e t a t i o n . 4 * / 5 r e t u r n _ t y p e f u n ct i o n _ n am e ( a r g 1 _ t y p e arg1_name , a r g 2 _ t y p e arg2_name ) 6 { 7 v a r i a b l e d e c l a r a t i o n s ; 8 9 f u n c t i o n s t a t e m e n t s ; 10 11 r e t u r n v a l u e ; 12 } ◮ All _name s must be valid identifiers ( A-Za-z_1-90 ). ◮ Each _type is a variable or class type ( int , double , ifstream ). ◮ function definition = The whole thing. ◮ function body = { variable declarations → return value; } ◮ function header = function definition- function body Function Anatomy Parts of a Function 2 / ** 3 * C a l c u l a t e t h e sq u a re r o o t o f a number . 4 * / 5 d o u b l e s q r t ( d o u b l e x ) 6 { 7 d o u b l e answer = _ _ m a c h i n e _ s p e c i f i c _ c o d e _ _ ; 8 r e t u r n answer ; 9 } ◮ The type of value returned matches the return_type . ◮ The variable x is a formal parameter of the sqrt function. ◮ Everything between the () of the function header is called the parameter declarations or argument list . ◮ sqrt : System library functions are used to insulate programmers from machine dependencies. Function Anatomy Parts of a Function 4 / ** 5 * P r i n t a " Hel l o World " message t o c o u t . 6 * / 7 v o i d s a y _ h e l l o _ w o r l d ( v o i d ) 8 { 9 c o u t << "Hello world , I’m a function!" << e n d l ; 10 r e t u r n ; 11 } ◮ The void as a return type indicates no return value....
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show_functions - CHAPTER 5 Programming with Functions...

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