   Introduction   Function Definition   Void function   Global Vs Local variables   Random Number Generator   Recurs...
   Experience has shown that the best way to develop and maintain large    programs is to construct it from smaller piece...
   In FORTRAN Modules Known as Subprograms   In Pascal Modules known as Procedures &    Functions   In C++ Modules Know...
      Functions invoked by a function–call-statement which consist of it’s         name and information it needs (argumen...
• Functions   called by writing        functionName (argument);        or        functionName(argument1, argument2, …);• E...
• Calling/invoking a function   – sqrt(x);   – Parentheses an operator used to call function       • Pass argument x      ...
Math Library Functions RevisitedMethod              Description                      Exampleceil( x )           rounds x t...
   Functions       Modularize a program       Software reusability          Call function multiple times   Local vari...
   Function prototype       Tells compiler argument type and return type of function       int square( int );         ...
   Syntax format for function definition    returned-value-type function-name (parameter-list)    {         Declarations ...
   Example function    int square( int y )    {        return y * y;    }   return keyword      Returns data, and contr...
// Creating and using a programmer-defined function.        #include <iostream.h>                                         ...
#include<iostream.h>int square(int); // prototype                        Outputint cube(int);   // prototype              ...
// Finding the maximum of three floating-point (real) numbers.    #include <iostream.h>    double maximum( double, double,...
   Function prototype contains      Function name      Parameters (number and data type)      Return type (void if ret...
If the Function does not RETURN result, it is called void Function       #include<iostream.h>       void add2Nums(int,int)...
If the function Does Not Take Arguments specify this with EMPT Y-LIST OR    write void inside     #include<iostream.h>    ...
   Local variables      Known only in the function in which they are       defined      All variables declared inside a...
   Omitting the type of returned result defaults to int, but    omitting a non-integer type is a Syntax Error   If a Glo...
#include<iostream.h>int x,y; //Global Variablesint add2(int, int); //prototypemain(){ int s;  x = 11;  y = 22;  cout << “g...
int sum(int x, int y){   int result;   result = x+y;}this function must return an integer value as indicated in the heade...
void f(float a);{  float a;  cout<<a<<endl;}   ; found after function definition header. redefining the parameter a in t...
void product(void){   int a, b, c, result;   cout << “enter three integers:”;   cin >> a >> b >> c;   result = a*b*c;   co...
       Call by value    •      A copy of the value is passed       Call by reference    •      The caller passes the add...
   Call By Reference   We introduce reference-parameter, to perform call by reference. The caller    gives the called fu...
#include<iostream.h>int squareVal(int); //prototype call by value functionvoid squareRef(int &); // prototype call by –ref...
   rand function generates an integer between 0 and RAND-    MAX(~32767) a symbolic constant defined in <stdlib.h>   You...
//generate 10 integers between 5…15int x;for ( int i=1; i<=10; i++){  x= rand()%11 + 5;  cout<<x<<“ “;}               ----...
    the rand( ) function will generate the same set of random    numbers each time you run the program .   To force NEW ...
#include<iostream.h>#include<iomanip.h>#include<stdlib.h>int main(){   int i;   unsigned num;   // we will enter a differe...
#include<iostream.h>#include<iomanip.h>#include<stdlib.h>int main(){   int i;    for(i=1; i<=5; i++)        cout<<setw(10)...
 Main calls another function…..normal A function calls another function2….normal A function calls itself ?! Possible?? ...
   A recursive function is called to solve a problem   The function knows to solve only the simplest cases    or so-call...
   Thus the function launches (calls) a fresh    copy of itself to work on the smaller    problem –this is related as a R...
5!                                   Final value=120                         5!                                5!=5*24=120...
//Recursive factorial Function#include<iostream.h>#include<iomonip.h>unsigned lion factorial(unsigned long);//prototypeint...
   Function overloading       Functions with same name and different        parameters       Should perform similar tas...
User defined functions
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User defined functions

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User defined functions

  1. 1.  Introduction Function Definition Void function Global Vs Local variables Random Number Generator Recursion Function Overloading Sample Code
  2. 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. 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. 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 WorkerWorker Worker Function ZFunction A Function B Worker Worker Note: usual main( ) Calls other Function B1 Function B2 functions, but other functions can call each other
  5. 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. 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. 7. Math Library Functions RevisitedMethod Description Exampleceil( x ) rounds x to the smallest integer ceil( 9.2 ) is 10.0 not less than x ceil( -9.8 ) is -9.0cos( 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 7.38906fabs( x ) absolute value of x fabs( 5.1 ) is 5.1 fabs( 0.0 ) is 0.0 fabs( -8.76 ) is 8.76floor( x ) rounds x to the largest integer floor( 9.2 ) is 9.0 not greater than x floor( -9.8 ) is -10.0fmod( x, y ) remainder of x/y as a floating- fmod( 13.657, 2.333 ) is 1.992 point numberlog( x ) natural logarithm of x (base e) log( 2.718282 ) is 1.0 log( 7.389056 ) is 2.0log10( x ) logarithm of x (base 10) log10( 10.0 ) is 1.0 log10( 100.0 ) is 2.0pow( x, y ) x raised to power y (xy) pow( 2, 7 ) is 128 pow( 9, .5 ) is 3sin( 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 3.0tan( x ) trigonometric tangent of x tan( 0.0 ) is 0 (x in radians)Fig. 3.2 Math library functions.
  8. 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. 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. 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. 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. 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. 13. #include<iostream.h>int square(int); // prototype Outputint cube(int); // prototype 1 square=1main() 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 functionint square(int y) //function definition{ return y*y; // returned Result}int cube(int y) //function definition{ return y*y*y; // returned Result}
  14. 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. 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. 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. 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. 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. 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. 20. #include<iostream.h>int x,y; //Global Variablesint add2(int, int); //prototypemain(){ 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=11int 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. 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. 22. void f(float a);{ float a; cout<<a<<endl;} ; found after function definition header. redefining the parameter a in the functionvoid f(float a){ float a2 = a + 8.9; cout <<a2<<endl;}
  23. 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. 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. 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. 26. #include<iostream.h>int squareVal(int); //prototype call by value functionvoid squareRef(int &); // prototype call by –reference functionint 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 squareValint 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 squareRefvoid squarRef(int &cRef){ cRef *= cRef; // caller’s argument modified}
  27. 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-rangeint x;for( int i=0; i<=10; i++){ x=rand(); cout<<x<<“ “;} -------------------------------------------------------//generate 10 integers between 0……..49int x;for( int i=0; i<10; i++){ x=rand()%50; cout<<x<<“ “;}
  28. 28. //generate 10 integers between 5…15int x;for ( int i=1; i<=10; i++){ x= rand()%11 + 5; cout<<x<<“ “;} ------------------------------------//generate 100 number as simulation of rolling a diceint x;for (int i=1; i<=100; i++){ x= rand%6 + 1; cout<<x<<“ “;}
  29. 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. 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 Runs19 6 1 1 4 2 118 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. 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 Runs5 3 3 5 4 25 3 3 5 4 2 Same set of numbers for5 3 3 5 4 25 3 3 5 4 2 each run6 5 3 3 5 4
  32. 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. 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 doesnt 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. 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. 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. 36. //Recursive factorial Function#include<iostream.h>#include<iomonip.h>unsigned lion factorial(unsigned long);//prototypeint 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. 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

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