Lecture 04Functions - I

METU Dept. of Computer Eng. Summer 2002Ceng230 - Section 01 Introduction To C Programmingby Ahmet Sacan

Wed July 8, 2002

re-glance @ TOC

• Variables, Data Types

• Conditionals: if, ?, switch

• Loops: for, while, do-while

• Functions

• Arrays

• Strings

#include <math.h>sin(x) sine of x

cos(x) cosine of x

tan(x) tan of x

asin(x) arcsine of x, result between -pi/2 and +pi/2

acos(x) arccosine of x, result between 0 and +pi

atan(x) arctan of x, result between -pi/2 and +pi/2

atan2(y,x) arctan of (y/x), result between -pi and +pi

hsin(x) hyperbolic sine of x

hcos(x) hyperbolic cosine of x

htan(x) hyperbolic tan of x

exp(x) exponential function

#include <math.h> (cont'd)

log(x) natural logarithm

log10(x) logarithm to base 10

pow(x,y) x to the power of y (x^y)

sqrt(x) the square root of x (x must not be negative)

ceil(x) ceiling; the smallest integer not less than x

floor(x) floor; the largest integer not greater than x

fabs(x) absolute value of x

ldexp(x,n) x times 2**n

frexp(x, int *exp) returns x normalized between 0.5 and 1; the exponent of 2 is in *exp

modf(x, double *ip) returns the fractional part of x; the integral part goes to *ip

fmod(x,y) returns the floating-point remainder of x/y, with the sign of x

math.h example

#include <math.h>#include <stdio.h>

void main ( ){ double d; int x; scanf("%lf", &d); printf("sqrt( ) = %lf\n", sqrt(d) ); x = ceil(d); printf("ceil ( ) = %d", x); printf("floor( ) = %d", floor(d) );}

Functions

• A function is a sub-program: section of a program designed to complete some tasks under the direction of another program unit.

• Using functions maximize:– modularity– readability

Function Declaration (Prototype)

<return-type> <function-name> ( <parameter-list> ) ;

• Function declaration gives the identity of the function. It tells the compiler how the function may be called.

• The prototype of a function f must occur either outside all functions and before any call to f, or inside all functions that call f.

Function Definition

<return-type> <function-name>

( <parameter-list> )

{

... <statements>

...}

functionhead

functionbody

Function Jargon

• Call a function:– transfer control to it. Execution continues from the

function. When function is done, the caller continues execution after the calling expression.

• Return value– determines the value of the calling expression.

• Parameters– declared in the function header.– Means of data exchange with the caller.

• Arguments– Declared in caller.– Correspond to function parameters.

Function Types

• with / without return-type.– void PrintIntro( );– int ReadAnInt( );

• with / without arguments.– void PrintIntro( );– void PrintResult( int res );

• type of arguments: readable, writeable...– int Add( int a, int b);

– void Add( int a, int b, int * sum);

Function exampleint mrFonk(int); /*prototype says: take an int, and return an int. */

void main(){ int x = 5, y;

y = mrFonk(x); /* function is called with argument: x */ /* return value of mrFunk is assigned to y */

}

int mrFonk(int b){ /* function header: almost identical to prototype. */

return ( b*b );}

functionbody

return value

Function exampleint mrFonk(int);

void main(){ int x = 5, y; printf("in main, before calling mrFunk(x): x=%d, y=%d\n", x, y); y = mrFonk(x);

printf("in main, after calling mrFunk(x): x=%d, y=%d\n", x, y);}

int mrFonk(int b){ printf("in mrFonk: b = %d\n", b); return ( b*b );}

different versions...

int mrFonk ( int );

void main( ) { int x = 5, y; y = mrFonk( x ); }

int mrFonk ( int b ) { return ( b*b );}

different versions...

void main() { int mrFonk( int ); int x = 5, y; y = mrFonk(x); }

int mrFonk (int b) { return ( b*b );}

different versions...

int mrFonk (int b) { return ( b*b );}

void main() {

int x = 5, y; y = mrFonk(x); }

more examples...double smaller ( double x, double y) {

return x < y ? x : y;

}

void main(){

...

c = smaller ( a, b);

...

}

more...

void PrintIntro( ){ printf("Welcome to my program.\n"); printf("I just learnt about functions.\n"); printf("So, here I'm using them...\n");}

void main ( ){ PrintIntro ( ); PrintIntro ( );}

simplest function...

void emptyHead ( ){

}

void main(){

emptyHead ( );

}

return what?

• you must return a value of the return-type.

double sqr(... ){

...

return x;

}

return void ?

• when return-type is void, return'ing is optional.

void PrintIntro(){

...

return;

}

Find 5 errors so it compiles...#include <studio.h>int main() { int num1, num2, int num3 = 5; char letter1 = 'a', letter2; num2 = num3 + 1; num1 = num2 x num2 + num3; letter2 = letter1; printf("The variable y equals %d\n," y); printf("The variable x equals %d\n", x); print("The variable z equals %d\n", z); printf("The variable letter1 equals %c \n", letter1); printf("The variable letter2 equals %c \n", letter2); return 0;}

if(x) if(y) z=1; else z=2;

i ii iii iv

X = 0 0 1 1

Y = 0 1 0 1

if(x) { if(y) z=1; } else z=2;

if(x) ; if(y) z=1; else z=2;

if(x && y) z=1; else z=2;

z = ?

Find equivalent

if ( x )if ( y )

if ( z ) humpty();else ;

else ;else

if ( y )if ( z )

dumpty( );else

bumpty( );else;

if ( x && y && z ) humpty ();else if ( y && z ) dumpty ( );else bumpty();

if ( x && y && z ) humpty ();else if ( !x && y && z ) dumpty();else if ( !x && y && !z) bumpty();

if ( y) if ( x && z ) humpty (); else if ( !x && z ) dumpty(); else if ( !x && !z) bumpty();