This document discusses function pointers, call by value, and call by reference. It defines a function pointer as storing the address of a function. It explains the steps to declare a function pointer and provides an example. It then describes call by value as copying the value of actual parameters into formal parameters, so changes within the function are not reflected in the original variables. Finally, it defines call by reference as passing the reference/address of the original variable, allowing the function to directly modify the original data.

1. Session – 19
Function pointer, call by value &
call by reference
Session Outcomes
• Function pointer or pointer to function
– Stores the address of a function
• Different methods of calling a function
– Call By Value
– Call By Reference

2. CALLING FUNCTION IN MAIN
void sum()
{
int a=2,b=3;
printf(“ answer =%d”, a+b);
}
int main()
{
void(*ptr) (void); // declaring function pointer
ptr=sum; // pointer storing address of function
ptr(); //calling of function written before main
}
Wednesday, June 10, 2020
For suggestions or queries contact
drkrk@kluniversity.in

3. STEPS TO DECLARE FUNCTION POINTER
• Declare the function pointer-
– Function pointer is declared by any name with precedence of *
operator.
– This pointer is written into opening closing rounded bracket.
– Return data type if any will be written first then pointer with
rounded brackets then data type of actual parameters will be
written in rounded brackets.
• Declaring function pointer does not means that function can be
directly called.
• Store the address- to call the function address of function must be
stored in function pointer
• Call the function using function pointer- instead of using function
name to call it now use function pointer name to call the function (if
arguments are there then pass it i.e. actual parameters)

4. Declaring a Function Pointer
Normal function:
void sum(int,int);
Its Function pointer:
void (*ptr)(int,int)
Wednesday, June 10, 2020
For suggestions or queries contact
drkrk@kluniversity.in
Return
type
Name of the
function
Argument (Actual
Parameters)
Explanation
void add (int , int ); Add is such a function which
accepts two integers and prints
addition of them
void (*ptr) (int, int); ptr is a pointer to such function
which accepts two integers.( the
function can do any thing. In this
case it will do addition)

5. Call by value
• Copies the value of actual parameters
into formal parameters.
• During execution whatever changes are
made in the formal parameters are not
reflected back in the actual parameters.

7. Call by Reference
• Reference(address) of the original variable is passed.
• Function does not create its own copy, it refers to the
original values by reference.
• Functions works with the original data and changes
are made in the original data.

9. Wednesday, June 10, 2020
For suggestions or queries contact
drkrk@kluniversity.in
Call by Reference
• Sometimes we need a function to return multiple
values.
• However, functions can only have one return value.
• One way to return multiple values is using reference
parameters.