Lecture 4 - C Functions

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Analytical and Computational Methods in Civil Engineering I1 st Semester A.Y. 2013-2014

Lecture 4 C Functions

Elvin B. CruzLecturer II

Institute of Civil Engineering


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Overview:- Functions in C Programming- Recursive Functions

- Math Functions- Scope and Lifetime of C Identifiers- Random Number Generation in C

CE 26 Lecture 4 C Functions


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Functions



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Functions

Types of Functions:

1. Standard library Functions

2. User-defined functions

Components:

1. Declaration2. Definition (body)



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Function Declaration

Introduces the name, return type, andparameters of a function

Must be done before calling the function

int myfunction ( float h, int y);


Return Type

FunctionName

Parameters


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Function Definition


Contains the executable statements of the function and

all its variable and their declarations

Functiondefinition ofthe main ()function


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#include

double r ( double x );

int main( ){

:disc = sqr ( b ) 4*a*c;

: }

double r ( double x ){

return (x*x) ;}

Example:



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Recursive Functions



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Recursive Functions

A recursive function is a function that calls itselfeither directly or indirectly through anotherfunction.

The function actually knows how to solve only thesimplest case(s), or so-called base case(s) . If thefunction is called with a base case, the functionsimply returns a result. If the function is called witha more complex problem, the function divides theproblem into pieces until it arrives with the basecase.



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CODE: OUTPUT:


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CODE: OUTPUT:


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Math Functions



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Math Functions


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Math Functions


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Scope and Lifetime ofC Identifiers



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a. File Scope

Such identifiers are known (i.e., accessible)in all functions from the point at which theidentifier is declared until the end of the file.

Global variables, function definitions, andfunction prototypes placed outside the mainfunction all have file scope.



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b. Block/Body Scope

Block scope ends at the terminating right brace (}) of theblock.

Local variables defined at the beginning of a functionhave block scope as do function parameters (inputs) ,which are considered local variables by the function.

Any block may contain variable definitions. When blocks

are nested, and an identifier in an outer block has thesame name as an identifier in an inner block, theidentifier in the outer block is hidden until the innerblock terminates.



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c. Function Scope (Labels)

Labels (an identifier followed by a colon suchas start: or stop:) are the only identifiers withfunction scope.

Labels can be used anywhere in the functionin which they appear, but cannot bereferenced outside the function body.

Labels are used in switch statements (as caselabels) and in goto statements



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Example: goto



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d. Function Prototype Scope

The only identifiers with function-prototype scope are thoseused in the parameter list of a function prototype.

Example:

void function(int x); // prototype -- x is a parameter

.

void function (int x) // declaration -- x is a parameter{Body statement }



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Random Number Generation



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rand ()- defined within

- rand () generates an integer between 0 andRAND_MAX(32767)

- If rand () truly produces integers at random,every number between 0 and RAND_MAXhasan equal chance (or probability) of beingchosen each time rand is called.



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srand( seed ); function defined within

function rand actually generates pseudorandomnumbers, hence, the sequence repeats itself each timethe program is executed

function srand takes an unsigned integer argument(seed) and seeds function rand to produce a different

sequence of random numbers for each execution of theprogram.

The function time() is commonly used as the seed of thesrand() function



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CODE:

OUTPUT:


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C Standard Library Header Files



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References:

C How to Program: Introducing C++ and Java,3 rd Ed. byDeitel&Deitel.

Lecture Notes and Presentations by Dr. EricTingatinga and Rahf Alvarez


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Lecture 4 - C Functions

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