1. -Neelima Singh PGT(CS) KV Sec-3 Rohini
Functions Calling
-Neelima Singh
PGT(CS)
KV Sec-3 Rohini

2. Contents Definition of functions Function calling Function definition
Void function
Remarks on function
Local v/s Global variables
Function call methods
Concept of recursion
Function overloading

3. Definition of functions
A function is a subprogram that acts on data and often returns a value.

4. Function Calling Function Arguments can be: Constant sqrt(9);
Functions called by writing
functionName (argument); or
functionName(argument1, argument2, …);
Example
cout << sqrt( );
sqrt (square root) function
The preceding statement would print 30
All functions in math library return a double
Function Arguments can be:
Constant sqrt(9);
Variable sqrt(x);
Expression sqrt( x*9 + y) ;
sqrt( sqrt(x) ) ;

5. Function Calling Calling/invoking a function sqrt(x);
Parentheses an operator used to call function
Pass argument x
Function gets its own copy of arguments
After finished, passes back result
Output
argument
Function Name 3
cout<< sqrt(9);
Parentheses used to enclose argument(s)

6. Functions Functions Local variables Parameters Modularize a program
Software reusability
Call function multiple times
Local variables
Known only in the function in which they are defined
All variables declared in function definitions are local variables
Parameters
Local variables passed to function when called
Provide outside information

7. Function Definition Function prototype Calling/invoking a function
Tells compiler argument type and return type of function
int square( int );
Function takes an int and returns an int
Explained in more detail later
Calling/invoking a function
square(x);
Parentheses an operator used to call function
Pass argument x
Function gets its own copy of arguments
After finished, passes back result

8. // Creating and using a programmer-defined function.
#include <iostream.h>
int square( int ); // function prototype
int main() {
// loop 10 times and calculate and output
// square of x each time
for ( int x = 1; x <= 10; x++ )
cout << square( x ) << " "; // function call
cout << endl;
return 0; // indicates successful termination
} // end main
Function prototype: specifies data types of arguments and return values. square expects an int, and returns an int.
Parentheses () cause function to be called. When done, it returns the result.
// square function definition returns square of an integer
int square( int y ) // y is a copy of argument to function {
return y * y; // returns square of y as an int
} // end function square
Definition of square. y is a copy of the argument passed. Returns y * y, or y squared.

9. Function maximum takes 3 arguments (all double) and returns a double.
} // end main
// function maximum definition. x, y and z are parameters
double maximum( double x, double y, double z ) {
double max = x; // assume x is largest
if ( y > max ) // if y is larger,
max = y; // assign y to max
if ( z > max ) // if z is larger,
max = z; // assign z to max
return max; // max is largest value
} // end function maximum
// Finding the maximum of three floating-point (real) numbers.
#include <iostream.h>
double maximum( double, double, double ); // function prototype
int main()
double number1, number2;
double number3;
cout << "Enter three real numbers: ";
cin >> number1 >> number2 >> number3;
// number1, number2 and number3 are arguments to the maximum function call
cout << "Maximum is: "
<< maximum( number1, number2, number3 ) << endl;
return 0; // indicates successful termination
Function maximum takes 3 arguments (all double) and returns a double.
Enter three real numbers:
Maximum is: 99.32
Enter three real numbers:
Maximum is: 3.333

10. Function Prototypes Function prototype contains
Function name
Parameters (number and data type)
Return type (void if returns nothing)
Only needed if function definition after function call
Prototype must match function definition
Function prototype
double maximum( double, double, double );
Definition
double maximum( double x, double y, double z ) { … }

11. Remarks on Functions Local variables Parameters
Known only in the function in which they are defined
All variables declared inside a function are local variables
Parameters
Local variables passed to function when called (passing- parameters)
Variables defined outside and before function main:
Called global variables
Can be accessible and used anywhere in the entire program

12. Local vs Global Variables
#include<iostream.h>
int x,y; //Global Variables
int add2(int, int); //prototype
main()
{ int s;
x = 11;
y = 22;
cout << “global x=” << x << endl;
cout << “Global y=” << y << endl;
s = add2(x, y);
cout << x << “+” << y << “=“ << s;
cout<<endl;
cout<<“\n---end of output---\n”;
return 0; }
int add2(int x1,int y1)
{ int x; //local variables
x=44;
cout << “\nLocal x=” << x << endl;
return x1+y1;
global x=11
global y=22
Local x=44
11+22=33
---end of output---

13. Function Call Methods Call by value Call by reference
A copy of the value is passed
Call by reference
The caller passes the address of the value
Up to this point all the calls we have seen are call-by-value, a copy of the value (known) is passed from the caller-function to the called- function
Any change to the copy does not affect the original value in the caller function
Advantages, prevents side effect, resulting in reliable software

14. Call by value method of accessing a function.
# include<iostream.h>
int main() {
int cube(int);
int vol, side=7;
vol=cube(side);
cout<<vol;
return 0; }
int cube (int a)
return a*a*a ;

15. Function Call Methods Call By Reference
We introduce reference-parameter, to perform call by reference. The caller gives the called function the ability to directly access the caller’s value, and to modify it.
A reference parameter is an alias for it’s corresponding argument, it is stated in c++ by “flow the parameter’s type” in the function prototype by an ampersand(&) also in the function definition-header.
Advantage: performance issue
void function_name (type &);// prototype
main() {
-----
------ }
void function_name(type &parameter_name)

16. value of orig in function change is : 20 value after change :-20
Example
# include<iostream.h>
int main() {
void change(int &);
int orig=10;
cout<<”origional value is “<<orig ;
change(orig);
cout<<”value after change( ) is over”<<orig ;
return 0; }
 void change(int &a)
a=20;
cout<<”value of orig in function change( ) is””
<<a;
return;
output:”
 the original value is :10
value of orig in function change is : 20
value after change :-20

17. THANKS