Part 3-functions
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    Part 3-functions Part 3-functions Presentation Transcript

    • C++ PROGRAMMING SKILLS Part 3 User-Defined Functions• Introduction• Function Definition• Void function• Global Vs Local variables• Random Number Generator• Recursion• Function Overloading• Sample Code
    • Functions in C++• 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; { } --- --- }
    • .)Functions in C++(Cont• 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
    • ++About Functions in C • 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
    • Function Calling• 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) ) ;
    • 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 Function Name argument Output 3 cout<< sqrt(9); Parentheses used to enclose argument(s)
    • 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.
    • Functions• 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
    • Function Definition• 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
    • Function Definition• 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)
    • Function Definition• 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
    • // 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
    • compute square and cube of numbers [1..10] using functions#include<iostream.h>int square(int); // prototype Outputint cube(int); // prototype 1 square=1main() 1 cube=1{ int i; 2 square=4 2 cube=8 for (int i=1;i<=10;i++){ . . 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}
    • // 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
    • 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 ) { … }
    • void Function takes argumentsIf 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; }
    • void Function take no argumentsIf the function Does Not Take Arguments specify this with EMPTY-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”; }
    • Remarks on Functions• 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
    • Remarks on Functions• 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
    • Local vs Global Variables#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”; global x=11 return 0;} global y=22int add2(int x1,int y1) Local x=44{ int x; //local variables 11+22=33 x=44; ---end of output--- cout << “nLocal x=” << x << endl; return x1+y1;}
    • Finding Errors in Function Codeint 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);
    • Finding Errors in Function Codevoid 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;}
    • Finding Errors in Function Codevoid 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;
    • Function Call Methods• 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
    • 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)
    • Function Call Example#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 squareVal} 4int squareVal(int a) x=2 after returning{ z=4 before calling squareRef return a*=a; // caller’s argument not modified z=16 after returning squareRef}void squarRef(int &cRef){ cRef *= cRef; // caller’s argument modified}
    • Random Number Generator• 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<<“ “;}
    • Random Number Generator//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<<“ “;}
    • Random Number Generator• 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
    • Randomizing with srand#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
    • without srand#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
    • Recursion and Recursive Functions• 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.
    • Concept Of recursion• 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
    • .(Concept Of recursion (cont• 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.
    • Finding Factorial Recursively5! 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
    • Finding Factorial Recursively//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);}
    • Function Overloading• 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