functions of C++
- 1. Name – Tarandeep Kaur Section – N2 Roll No. – 115331
- 2. 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. A function is a subprogram that acts on data and often returns a value.
- 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. 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
- 8. 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
- 9. 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
- 10. // 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 { // loop 10 times and calculate and output an int. // square of x each time for ( int x = 1; x <= 10; x++ ) cout << square( x ) << " "; // function call cout << endl; Parentheses () cause function to be called. 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
- 11. // 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
- 12. 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 ) { … }
- 13. 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; }
- 14. If 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”; }
- 15. 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
- 16. #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) global y=22 { int x; //local variables Local x=44 x=44; 11+22=33 cout << “nLocal x=” << x << endl; return x1+y1; ---end of output--- }
- 17. 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
- 18. 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 ¶meter_name)
- 19. #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 }
- 20. 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.
- 21. 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
- 22. 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
- 23. THANKS