The document discusses functions in C programming. It covers defining and calling functions, passing arguments to functions, return statements, and different types of functions. Some key points include: - Functions make code modular and reusable. Arguments can be passed by value or reference. - A function is defined with a return type, name, and parameters. It is called by name with arguments. Return passes data back to the calling function. - Functions can take arguments and return values, take arguments but not return, return values without arguments, or do neither. - Arguments are passed right to left in C. Functions can be nested by calling one function from another.

1. Functions
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2. 08/23/152

3. Advantages :
 Program writing becomes easy
 Program becomes easy to understand
 Modification in large program becomes easy
 Modularity comes in program when we use function
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4. Calling to a function.
message();
main( )
{
message( ) ;
printf ( "nHello!" ) ;
}
message( )
{
printf ( "nJUET..." ) ;
}
And here’s the output...
JUET
Hello! 08/23/154

5. Calling to a function(Cont…)
When main function calls message() the control passes to the
function message( ). The activity of main( ) is temporarily
suspended; it falls asleep while the message( ) function wakes up and
goes to work. When the message( ) function runs out of statements
to execute, the control returns to main( ), which comes to life again
and begins executing its code at the exact point where it left off.
Thus, main( ) becomes the ‘calling’ function, whereas message( )
becomes the ‘called’ function.
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6. Cont…
main( )
{
printf ( "nI am in main" ) ;
italy( ) ;
brazil( ) ;
argentina( ) ;
}
italy( ){
printf ( "nI am in italy" ) ;
}
brazil( ){
printf ( "nI am in brazil" ) ;
}
argentina( ){
printf ( "nI am in argentina" ) ;
}
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I am in main
I am in italy
I am in brazil
I am in argentina

7. Function Declaration
Declaration Syntax:
Return_Type Function_Name(argument_list);
 Return_Type can be any of data type like char, int, float, double,
array, pointer etc.
 argument_list can also be any of data type like char, int, float,
double, array, pointer etc.
 Declaration must be before the call of function in main
function
Example: int add(int a, int b);
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8. Function Definition
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9. Function Call
Call Syntax:
Function_Name(argument_list);
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10. Sample Example
#include<stdio.h>
int sum (int,int); //function declaration
void main(){
int p;
p=sum(3,4); //function call
printf(“%d”,p);
}
int sum( int a,int b){
int s; //function body
s=a+b;
return s; //function returning a value
} 08/23/1510

11. Passing arguments to functions
In programming, argument(parameter) refers to data that is
passed to function(function definition) while calling function.
In following example two variable, num1 and num2 are passed to
function during function call and these arguments are accepted by
arguments a and b in function definition.
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12. Cont…
 Formal Parameter :Parameter written in Function Definition is Called “Formal
Parameter”.
 In last example a and b are formal parameters.
 There are two methods of declaring the formal arguments.
1. Kernighan and Ritchie (or just K & R) method.
calsum ( x, y, z )
int x, y, z ;
2. ANSI method
calsum ( int x, int y, int z )
 This method is called ANSI method and is more commonlyused these days.
 Actual Parameter :Parameter written in Function Call is Called “Actual
Parameter”.
 In last example num1 and num2 were actual parameters. 08/23/1512

13. Example: parameter passing
/* Sending and receiving values between functions */
main( ){
int a, b, c, sum ;
printf ( "nEnter any three numbers " ) ;
scanf ( "%d %d %d", &a, &b, &c ) ;
sum = calsum ( a, b, c ) ;
printf ( "nSum = %d", sum ) ;
}
calsum ( x, y, z )
int x, y, z ;
{
int d ;
d = x + y + z ;
return ( d ) ;
}
And here is the output...
Enter any three numbers 10 20 30
Sum = 60 08/23/1513

14. Return statement
In the message() function of previous example the moment closing
brace ( } ) of the called function was encountered the control returned
to the calling function. No separate return statement was necessary to
send back the control.
This approach is fine if the called function is not going to return any
meaningful value to the calling function.
In the above program, however, we want to return the sum of x, y
and z. Therefore, it is necessary to use the return statement.
 The return statement serves two purposes:
(1) On executing the return statement it immediately transfers the control back to the
calling program.
(2) It returns the value present in the parentheses after return, to the calling function.
In the above program the value of sum of three numbers is being returned.
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15. Return statement(Cont…)
 There is no restriction on the number of return statements that may be present in a
function. Also, the return statement need not always be present at the end of the
called function.
 The following program illustrates these facts.
fun( ){
char ch ;
printf ( "nEnter any alphabet " ) ;
scanf ( "%c", &ch ) ;
if ( ch >= 65 && ch <= 90 )
return ( ch ) ;
else
return ( ch + 32 ) ;
}
 In this function different return statements will be executed depending on whether
ch is capital or not.
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16. Return statement(Cont…)
 If a meaningful value is returned then it should be accepted in the calling program by
equating the called function to some variable. For example,
 sum = calsum ( a, b, c ) ;
 All the following are valid return statements.
 return ( a ) ;
 return ( 23 ) ;
 return ( 12.34 ) ;
 return ;
 A function can return only one value at a time. Thus, the following statements are
invalid.
return ( a, b ) ;//this will return value of b
return ( x, 12 ) ;
 There is a way to get around this limitation, which would be discussed later when we
learn pointers.
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17. Calling Convention
Calling convention indicates the order in which arguments are
passed to a function when a function call is encountered. There
are two possibilities here:
(a) Arguments might be passed from left to right.
(b) Arguments might be passed from right to left.
C language follows the second order.
Consider the following function call:
fun (a, b, c, d ) ;
In this call it doesn’t matter whether the arguments are passed
from left to right or from right to left.
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18. Calling Convention(Cont…)
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•However, in some function call the order of passing arguments
becomes an important consideration.
•For example:

19. Ways to Pass Parameters
Call By Value:In this approach we pass copy of actual variables
in function as a parameter.
Hence any modification on parameters inside the function will not
reflect in the actual variable.
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20. Ways to Pass
Parameters(Cont..)
Call By Reference:In this approach we pass memory address of
actual variables in function as a parameter.
Hence any modification on parameters inside the function will
reflect in the actual variable.
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21. Swap two variables without using a
third variable
#include<stdio.h>
void swap(int *,int *);
void main(){
int a=5,b=10;
swap(&a,&b);
printf("%d %d",a,b);
}
void swap(int *a,int *b){
*a=*a+*b;
*b=*a-*b;
*a=*a-*b;
}

22. Types of Function
1st :Take something and Return something (Function
with return value and parameters)
Example: printf, scanf , strlen, strcmp etc.
2nd : Take something and Return nothing (Function
with no return value but parameters)
Example: delay,
3rd : Take nothing and return something (Function with
return value but no parameter)
Example: getch,
4th : Take nothing and return nothing (Function with
no return value and no parameter)
Example: clrscr,
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23. Take something and Return
something
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24. Take something and Return
nothing
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25. Take nothing and return
something
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26. Take nothing and return
nothing
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27. Nesting of function call
 If we are calling any function inside another function call is known as nesting
function call.
 Sometime it converts a difficult program in easy one.
 For example 1:
int max(int x,int y){
return x>y?x:y;
}
int fact(int);
void main(){
int a,b,c;
scanf(“%d%d”,&a,&b);
c=fact(max(a,b));
print(“factorial of %d is %d”,max(a,b),c);
}
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int fact(int a)
{
int fact=1;
while(a>0)
{
fact=fact*a;
a--;
}
return fact;
}
O/P:6
7
factorial of 7 is 5040

28. Example 2 Nested calling
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29. Problem
Write a function which receives a float and an int from
main( ), finds the product of these two and returns the
product which is printed through main( ).
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