Lecture 04 Functions I

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Lecture 04Functions - I
Wed July 8, 2002

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

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re-glance _at_ TOC

• Variables, Data Types
• Conditionals if, ?, switch
• Loops for, while, do-while
• Functions
• Arrays
• Strings

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include ltmath.hgt
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include ltmath.hgt (cont'd)
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math.h example

• include ltmath.hgt
• include ltstdio.hgt
• 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) )

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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

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Function Declaration (Prototype)

• ltreturn-typegt ltfunction-namegt
• ( ltparameter-listgt )
• 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.

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Function Definition

• ltreturn-typegt ltfunction-namegt
• ( ltparameter-listgt )
• ...
• ltstatementsgt
• ...

function head
function body
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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.

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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)

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Function example

• int 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 ( bb )

function body
return value
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Function example

• int mrFonk(int)
• void main()
• int x 5, y
• printf("in main, before calling mrFunk(x)
  xd, yd\n", x, y)
• y mrFonk(x)
• printf("in main, after calling mrFunk(x)
  xd, yd\n", x, y)
• int mrFonk(int b)
• printf("in mrFonk b d\n", b)
• return ( bb )

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different versions...

• int mrFonk ( int )
• void main( )
• int x 5, y
• y mrFonk( x )
• int mrFonk ( int b )
• return ( bb )

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different versions...

• void main()
• int mrFonk( int )
• int x 5, y
• y mrFonk(x)
• int mrFonk (int b)
• return ( bb )

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different versions...

• int mrFonk (int b)
• return ( bb )
• void main()
• int x 5, y
• y mrFonk(x)

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more examples...

• double smaller ( double x, double y)
• return x lt y ? x y
• void main()
• ...
• c smaller ( a, b)
• ...

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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 ( )

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simplest function...

• void emptyHead ( )
• void main()
• emptyHead ( )

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return what?

• you must return a value of the return-type.
• double sqr(... )
• ...
• return x

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return void ?

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

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Find 5 errors so it compiles...

• include ltstudio.hgt
• 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

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• if(x)
• if(y)
• z1
• else
• z2

if(x) if(y) z1 else z2
if(x) if(y) z1 else z2
if(x y) z1 else z2
z ?
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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()