The document discusses functions in C++. It defines functions as modules that can be called to break programs into smaller pieces, making code easier to design, build, debug and maintain. It provides examples of function definitions and calls. Functions take arguments, make copies of them, perform tasks, and return results. Function prototypes specify argument and return types. Well-designed programs use preexisting and new functions to organize and reuse code.

1.  Introduction
 Function Definition
 Void function
 Global Vs Local variables
 Random Number Generator
 Recursion
 Function Overloading
 Sample Code

2.  Experience has shown that the best way to develop and maintain large
programs is to construct it from smaller pieces(Modules)
 This technique Called “Divide and Conquer”
Bad Development Approach Wise Development Approach
main()
main() •Easer To {
{ -----
----- Design ----
----- Build }
----- Debug
----- Extend function f1()
. Modify {
. Understand ---
. Reuse ---
---- Better Organization }
-----
----- function f2()
Return 0; {
} ---
---
}

3.  In FORTRAN Modules Known as Subprograms
 In Pascal Modules known as Procedures &
Functions
 In C++ Modules Known as Functions & Classes
 Programs use new and “prepackaged” modules
 New: programmer-defined functions and classes
 Prepackaged: from the standard library

4.  Functions invoked by a function–call-statement which consist of it’s
name and information it needs (arguments)
 Boss To Worker Analogy
 A Boss (the calling/caller function) asks a worker (the called
function) to perform a task and return result when it is done.
Boss
Main
Worker
Worker Worker
Function Z
Function A Function B
Worker Worker
Note: usual main( ) Calls other
Function B1 Function B2 functions, but other functions
can call each other

5. • Functions called by writing
functionName (argument);
or
functionName(argument1, argument2, …);
• Example
cout << sqrt( 900.0 );
• 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) ) ;

6. • 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
Function Name argument Output
3
cout<< sqrt(9);
Parentheses used to enclose argument(s)

7. Math Library Functions Revisited
Method Description Example
ceil( x ) rounds x to the smallest integer ceil( 9.2 ) is 10.0
not less than x ceil( -9.8 ) is -9.0
cos( x ) trigonometric cosine of x cos( 0.0 ) is 1.0
(x in radians)
exp( x ) exponential function ex exp( 1.0 ) is 2.71828
exp( 2.0 ) is 7.38906
fabs( x ) absolute value of x fabs( 5.1 ) is 5.1
fabs( 0.0 ) is 0.0
fabs( -8.76 ) is 8.76
floor( x ) rounds x to the largest integer floor( 9.2 ) is 9.0
not greater than x floor( -9.8 ) is -10.0
fmod( x, y ) remainder of x/y as a floating- fmod( 13.657, 2.333 ) is 1.992
point number
log( x ) natural logarithm of x (base e) log( 2.718282 ) is 1.0
log( 7.389056 ) is 2.0
log10( x ) logarithm of x (base 10) log10( 10.0 ) is 1.0
log10( 100.0 ) is 2.0
pow( x, y ) x raised to power y (xy) pow( 2, 7 ) is 128
pow( 9, .5 ) is 3
sin( x ) trigonometric sine of x sin( 0.0 ) is 0
(x in radians)
sqrt( x ) square root of x sqrt( 900.0 ) is 30.0
sqrt( 9.0 ) is 3.0
tan( x ) trigonometric tangent of x tan( 0.0 ) is 0
(x in radians)
Fig. 3.2 Math library functions.

8.  Functions
 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

9.  Function prototype
 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

10.  Syntax format for function definition
returned-value-type function-name (parameter-list)
{
Declarations of local variables and Statements
}
 Parameter list
 Comma separated list of arguments
 Data type needed for each argument
 If no arguments, use void or leave blank
 Return-value-type
 Data type of result returned (use void if nothing
returned)

11.  Example function
int square( int y )
{
return y * y;
}
 return keyword
 Returns data, and control goes to function’s
caller
 If no data to return, use return;
 Function ends when reaches right brace
 Control goes to caller
 Functions cannot be defined inside other functions

12. // Creating and using a programmer-defined function.
#include <iostream.h>
Function prototype: specifies
int square( int ); // function prototype data types of arguments and
return values. square
int main()
expects an int, and returns
{
an int.
// loop 10 times and calculate and output
// square of x each time
for ( int x = 1; x <= 10; x++ )
cout << square( x ) << " "; // function call
Parentheses () cause function to be called.
cout << endl;
When done, it returns the result.
return 0; // indicates successful termination
} // end main
// 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
Definition of square. y is a
copy of the argument passed.
} // end function square Returns y * y, or y squared.
1 4 9 16 25 36 49 64 81 100

13. #include<iostream.h>
int square(int); // prototype Output
int cube(int); // prototype 1 square=1
main() 1 cube=1
{ int i; 2 square=4
for (int i=1;i<=10;i++){ 2 cube=8
.
.
cout<< i<< “square=“ << square(i) << endl;
.
cout<< i<< “cube=“ <<cube(i) << endl; .
} // end for 10 square=100
return 0; 10 cube=1000
} // end main function
int square(int y) //function definition
{
return y*y; // returned Result
}
int cube(int y) //function definition
{
return y*y*y; // returned Result
}

14. // 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; Function maximum takes 3
arguments (all double) and
cout << "Enter three real numbers: "; returns a double.
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
} // 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 Enter three real numbers: 99.32 37.3 27.1928
if ( y > max ) // if y is larger, Maximum is: 99.32
max = y; // assign y to max
Enter three real numbers: 1.1 3.333 2.22
if ( z > max ) // if z is larger,
Maximum is: 3.333
max = z; // assign z to max
return max; // max is largest value
} // end function maximum

15.  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 )
{
…
}

16. If the Function does not RETURN result, it is called void Function
#include<iostream.h>
void add2Nums(int,int);
main()
{ int a, b;
cout<<“enter tow Number:”;
cin >>a >> b;
add2Nums(a, b)
return 0;
}
void add2Nums(int x, int y)
{
cout<< x<< “+” << y << “=“ << x+y;
}

17. If the function Does Not Take Arguments specify this with EMPT Y-LIST OR
write void inside
#include<iostream.h>
void funA();
void funB(void)
main()
{ Will be the same
funA(); in all cases
funB();
return 0;
}
void funA()
{
cout << “Function-A takes no arqumentsn”;
}
void funB()
{
cout << “Also Function-B takes No argumentsn”;
}

18.  Local variables
 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

19.  Omitting the type of returned result defaults to int, but
omitting a non-integer type is a Syntax Error
 If a Global variable defined again as a local variable in a
function, then the Local-definition overrides the Global
defining
 Function prototype, function definition, and function call
must be consistent in:
1- Number of arguments
2- Type of those arguments
3-Order of those arguments

20. #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;
} global x=11
int add2(int x1,int y1)
{ int x; //local variables global y=22
x=44; Local x=44
cout << “nLocal x=” << x << endl; 11+22=33
return x1+y1;
}
---end of output---

21. int sum(int x, int y)
{
int result;
result = x+y;
}
this function must return an integer value as indicated in the header
definition (return result;) should be added
----------------------------------------------------------------------------------------
-
int sum (int n)
{ if (n==0)
return 0;
else
n+sum(n-1);
}
the result of n+sum(n-1) is not returned; sum returns an improper
result, the else part should be written as:-
else return n+sum(n-1);

22. void f(float a);
{
float a;
cout<<a<<endl;
}
 ; found after function definition header.
 redefining the parameter a in the function
void f(float a)
{
float a2 = a + 8.9;
cout <<a2<<endl;
}

23. void product(void)
{
int a, b, c, result;
cout << “enter three integers:”;
cin >> a >> b >> c;
result = a*b*c;
cout << “Result is” << result;
return result;
}
 According to the definition it should not return a value , but in the block (body) it
did & this is WRONG.
  Remove return Result;

24.  Call by value
• A copy of the value is passed
 Call by reference
• The caller passes the address of the value
 Call by 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

25.  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)

26. #include<iostream.h>
int squareVal(int); //prototype call by value function
void squareRef(int &); // prototype call by –reference function
int main()
{ int x=2; z=4;
cout<< “x=“ << x << “before calling squareVal”;
cout << “n” << squareVal(x) << “n”; // call by value
cout<< “x=“ << x << “After returning”
cout<< “z=“ << z << “before calling squareRef”;
squareRef(z); // call by reference
cout<< “z=“ << z<< “After returning squareRef”
return 0;
} x=2 before calling squareVal
int squareVal(int a) 4
{ x=2 after returning
return a*=a; // caller’s argument not modified z=4 before calling squareRef
} z=16 after returning squareRef
void squarRef(int &cRef)
{
cRef *= cRef; // caller’s argument modified
}

27.  rand function generates an integer between 0 and RAND-
MAX(~32767) a symbolic constant defined in <stdlib.h>
 You may use modulus operator (%) to generate numbers within a
specifically range with rand.
//generate 10 random numbers open-range
int x;
for( int i=0; i<=10; i++){
x=rand();
cout<<x<<“ “;
}
-------------------------------------------------------
//generate 10 integers between 0……..49
int x;
for( int i=0; i<10; i++){
x=rand()%50;
cout<<x<<“ “;
}

28. //generate 10 integers between 5…15
int x;
for ( int i=1; i<=10; i++){
x= rand()%11 + 5;
cout<<x<<“ “;
}
------------------------------------
//generate 100 number as simulation of rolling a
dice
int x;
for (int i=1; i<=100; i++){
x= rand%6 + 1;
cout<<x<<“ “;
}

29.  the rand( ) function will generate the same set of random
numbers each time you run the program .
 To force NEW set of random numbers with each new run
use the randomizing process
 Randomizing is accomplished with the standard library
function srand(unsigned integer); which needs a
header file <stdlib.h>
Explanation of signed and unsigned integers:
 int is stored in at least two-bytes of memory and can
have positive & negative values
 unsigned int also stored in at least two-bytes of
memory but it can have only positive values 0…..65535

30. #include<iostream.h>
#include<iomanip.h>
#include<stdlib.h>
int main()
{
int i;
unsigned num;
// we will enter a different number each time we run
cin>>num;
srand(num);
for(i=1; i<=5; i++)
cout<<setw(10)<< 1+rand()%6;
return 0;
}
Output for Multiple Runs
19 6 1 1 4 2 1
18 6 1 5 1 4 4 Different-set of Random
3 1 2 5 6 2 4 numbers
0 1 5 5 3 5 5
3 1 2 5 6 3 4

31. #include<iostream.h>
#include<iomanip.h>
#include<stdlib.h>
int main()
{
int i;
for(i=1; i<=5; i++)
cout<<setw(10)<< 1+rand()%6;
return 0;
}
Output for Multiple Runs
5 3 3 5 4 2
5 3 3 5 4 2 Same set of numbers for
5 3 3 5 4 2
5 3 3 5 4 2
each run
6 5 3 3 5 4

32.  Main calls another function…..normal
 A function calls another function2….normal
 A function calls itself ?! Possible?? YES
A recursive function is one that call itself.

33.  A recursive function is called to solve a problem
 The function knows to solve only the simplest cases
or so-called base-cases
 Thus if the function called with a base-case, it simply
returns a result. But if it is called with more complex
problem, the function divides the problem into two
conceptual pieces, one knows how to do, and another
doesn't know what to do.
 The second case/piece must resemble the original
problem, but be a slightly simpler/smaller version of
the original problem

34.  Thus the function launches (calls) a fresh
copy of itself to work on the smaller
problem –this is related as a Recursive-
call/recursive step.
 The function keeps dividing each new sub
problem into two conceptual pieces until
eventually terminates after converging on
the base-case.
 The function thus recognize the base-case
and returns a result to the previous copy of
the way up the line until original call of the
function returns the final result to main.

35. 5! Final value=120
5!
5!=5*24=120 returned
5*4! 5*4!
4!=4*6=24 returned
4*3! 4*3!
3!=3*2=6 returned
3*2! 3*2!
2!=2*1=2 returned
2*1! 2*1!
1
1 1

36. //Recursive factorial Function
#include<iostream.h>
#include<iomonip.h>
unsigned lion factorial(unsigned long);//prototype
int main()
{
int num;
cout<<“enter a positive integer:”;
cin>>num;
cout<<“factorial=“<<factorial(num);
return 0;
}
unsigned long factorial(unsigned long n)
{
if ( n <= 1) //the base case
return 1;
else
return n * factorial (n - 1);
}

37.  Function overloading
 Functions with same name and different
parameters
 Should perform similar tasks
 I.e., function to square ints and function to square floats
int square( int x) {return x * x;}
float square(float x) { return x * x; }
 A call-time c++ complier selects the proper function by
examining the number, type and order of the parameters