Lec 09. Introduction to Functions / Call by Values

Lecture 9Lecture 9
Version 1.0Version 1.0
Introduction to FunctionsIntroduction to Functions
Call by ValueCall by Value

2Rushdi Shams, Dept of CSE, KUET, Bangladesh
 We have already known that in a C program,We have already known that in a C program,
there must be a main () functionthere must be a main () function
 In C, we used many library functions as well-In C, we used many library functions as well-
printf (), scanf (), clrscr (), or getch ()printf (), scanf (), clrscr (), or getch ()
 printf() prints on the outputprintf() prints on the output
 scanf () takes input from the user and assignsscanf () takes input from the user and assigns
that input to a variable by going to the variable’sthat input to a variable by going to the variable’s
addressaddress

 clrscr () clears the output bufferclrscr () clears the output buffer
 getch () waits for a key-stroke from the usergetch () waits for a key-stroke from the user
 if you think uniform one thing is common toif you think uniform one thing is common to
say- the function does one particular job. Isn’tsay- the function does one particular job. Isn’t
it?it?

 In C, user can define functions as well- as manyIn C, user can define functions as well- as many
functions as they wish. These functions arefunctions as they wish. These functions are
called user defined functionscalled user defined functions

Example of FunctionExample of Function

Another ExampleAnother Example

What We have learnt?What We have learnt?
 There is no limit on the number of functionsThere is no limit on the number of functions
that might be present in a C program.that might be present in a C program.
 Each function in a program is called in theEach function in a program is called in the
sequence specified by the function calls.sequence specified by the function calls.
 After each function has done its job, controlAfter each function has done its job, control
returns to the place of calling that function.returns to the place of calling that function.

 Well, then, should all the function calls takeWell, then, should all the function calls take
place inside the main () function? No! Functionsplace inside the main () function? No! Functions
defined by the user can call other functions asdefined by the user can call other functions as
well.well.

We have known a lot!!We have known a lot!!
 C program is a collection of one or more functions.C program is a collection of one or more functions.
 A function gets called when the function name isA function gets called when the function name is
followed by a semicolon.followed by a semicolon.

 A function is defined when function name is followedA function is defined when function name is followed
by a pair of braces in which one or more statementsby a pair of braces in which one or more statements
may be present.may be present.

 Any function can be called from any other function.Any function can be called from any other function.
EvenEven main( )main( ) can be called from other functions.can be called from other functions.

 A function can be called any number of times.A function can be called any number of times.

 The order in which the functions are defined in aThe order in which the functions are defined in a
program and the order in which they get called needprogram and the order in which they get called need
not necessarily be samenot necessarily be same

 A function can be called from other function, but aA function can be called from other function, but a
function cannot be defined in another function. Thus,function cannot be defined in another function. Thus,
the following program code would be wrong, sincethe following program code would be wrong, since
argentina( )argentina( ) is being defined inside another function,is being defined inside another function,
main( )main( )..

 There are basically two types of functions:There are basically two types of functions:
 Library functions Ex.Library functions Ex. printf( )printf( ),, scanf( )scanf( ) etc.etc.
 User-defined functions Ex.User-defined functions Ex. argentina( )argentina( ),,
brazil( )brazil( ) etc.etc.

 Function Declaration or function prototypingFunction Declaration or function prototyping
 Function Definition or function bodyFunction Definition or function body
 The basic format of function definition is-The basic format of function definition is-

 We have seen only void as the return-type in functionsWe have seen only void as the return-type in functions
so far. But it can be of any valid C data type. It specifiesso far. But it can be of any valid C data type. It specifies
what type of data the function will hand over to thewhat type of data the function will hand over to the
callercaller
 Parameter-list is a comma separated list containingParameter-list is a comma separated list containing
declaration of parameters received by the functiondeclaration of parameters received by the function
when it is called. We have also seen only void in thewhen it is called. We have also seen only void in the
parameter-lists so far (it means the function does notparameter-lists so far (it means the function does not
get any value from the caller)get any value from the caller)

10,20,30
maximum(10,20,30)
maximum(10,20,30)

Lec 09. Introduction to Functions / Call by Values

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