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Function

Function. User defined function is a code segment (block) that perform an specific action. Function Definition: Return_DT F_name ( list of formal parameters) { Action_ body ; }. The Function Definition. Function are of 4 types:

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Function

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  1. Function User defined function is a code segment (block) that perform an specific action. Function Definition:Return_DT F_name ( list of formal parameters) { Action_ body ; }

  2. The Function Definition Function are of 4 types: 1- A function that doesn’t return a value without argument -Return_DT is void -Action_body doesn’t contain return statement. Syntax: void function-name ( ) { local declarations // this is optional executable statements }

  3. Example: function that doesn’t return a value without arguments void print_O ( ) { cout << “ ** “ << endl; cout << “ * * “ << endl; cout << “ * * “ << endl; cout << “ ** “ << endl; }

  4. The Function Definition 2- A function that doesn’t return a value with arguments -Return_DT is void -Action_body doesn’t contain return statement. Syntax: void function-name(argument_list) { local declarations // this is optional executable statements }

  5. Example: function that doesn’t return a value with arguments void print_box (int n) { cout << “* * * * * * *\n” ; cout << “* “ << n << “ * \n” ; cout << “* * * * * * *\n” ; }

  6. The Function Definition 3- A function that returns a result of any type without arguments -Return_DT is any type -Action_body contains return statement. Syntax: <any type> function-name( ) { local declarations // this is optional executable statements }

  7. Example: function that return a value without arguments int sum () { int x=5, y=7 ; return x+y ; }

  8. The Function Definition 4- A function that returns a result of any type with arguments -Return_DT is any type -Action_body contains return statement. Syntax: <any type> function-name(argument_list ) { local declarations // this is optional executable statements }

  9. Example: function that return a value with arguments int Rect_area (int L, int W) { int a ; a = L * W ; return a ; }

  10. Calling (invoking) Function: a) The call to a Function that does not return a value is given in the following syntax: F_name (Actual parameters); e.g. draw_circle ( ); e.g. sum(4,7); b) The call to a Function that returns a value is given as follows: - The name of the functio is given within the output statement e.g cout<<sum(x,y); - The name of the Function is given within the assignment statement e.g. result = sum (x, y );

  11. The Call to a function program Figure Function draw_circle void main(){ ------- ------- draw_circle ( ); ------ ------ ------ } void draw_circle ( ) { ------ ------ ------ ------ } call return

  12. Example #include <iostream.h> int Max (int Value1, int Value2) { if (Value1 > Value2) return Value1; else return Value2; } void main() { int a, b; cout<<"\nPlease Enter the values of a and b: "; cin>>a>>b; cout<<"\n the maximum one is: "<<Max(a,b)<<endl; } Function Definition Calling the function in an expression like cout<<, condition, assignment statements

  13. Example #include <iostream.h> int Max (int Value1, int Value2) { if (Value1 > Value2) return Value1; else return Value2; } void main() { int a, b; cout<<"\nPlease Enter the values of a and b: "; cin>>a>>b; cout<<"\n the maximum one is: "<<Max(a,b)<<endl; }

  14. Example #include <iostream.h> int Sum (int A, int B) { return (A+B); } void main() { int N1, N2, S; cout<<"\n Please Enter N1 and N2: "; cin>>N1>>N2; S = Sum(N1,N2); cout<<"\nSum= "<<S<<endl; }

  15. Example #include <iostream.h> bool Positive (int Num) { if (Num > 0) return true; else return false; } void main() { int Number; cout<<"\nEnter Number: "; cin>> Number; if (Positive(Number)) cout<<"\n the number is positive"; else cout<<"\n the number is negative"; cout<<endl; }

  16. Example #include <iostream.h> float Area (int R) { return (3.14 * R * R ); } void main() { int Radius; cout<<"Enter the Redius: "; cin>>Radius; cout<<"\nCircle Area is: "<<Area(Radius); cout<<endl; }

  17. Example #include <iostream.h> long Power(int Base, int Exp) { int M=1; for(int i=1; i<=Exp; i++) M*=Base; return M; } void main() { int B, E; cout<<"\nEnter Base: "; cin>>B; cout<<"\nEnter Exponent: "; cin>>E; cout<<"\n Result= "<<Power(B,E); cout<<endl; }

  18. Example #include <iostream.h> long Fact (int Num) { int F = 1, i = Num; while (i>=1){ F *= i; i--; } return F; } void main() { int Number; cout<<"Enter an integer number: "; cin>>Number; cout<<endl<<Number<<"!= "<<Fact(Number); cout<<endl; }

  19. Void Returned Data Type #include <iostream.h> void Print(char Ch, int n) { for (int i=1; i<=n; i++) cout<<Ch; cout<<endl; } void main() { char Sym; int Number; cout<<"\nEnter the Symbol: "; cin>>Sym; cout<<"\nHow many times: "; cin>>Number; Print(Sym,Number); } No Return Statement

  20. Example #include <iostream.h> int Mul(int V1, int V2) { return V1 * V2; } void Result() { cout<<"\n5 x 9 = "<<Mul(5,9); cout<<"\n4 x 7 = "<<Mul(4,7); cout<<"\n6 x 4 = "<<Mul(6,4)<<endl; } void main() { Result() ; }

  21. The Function Prototype • Like other identifiers in C++, function must be declared before it can be referenced. • To declare a function, we can insert a function prototype before the main function. • The function prototype provides all information that the C++ compiler needs to know to translate calls to the function correctly. • A function prototype tells the compiler the - data type of the function - the function name - information about the arguments that the function expects. • Examples: void draw_circle ( ); int m ( ) ; void print_box (int) ; int Rect_area (int , int);

  22. Function Prototype #include <iostream.h> int Mul(int, int); int Add(int, int); void Show(); void main() { Show(); } int Mul(int X, int Y) { return X*Y; } int Add(int X, int Y) { return X+Y; } void Show() { int A=10, B=20; cout<<Add(A,B)<<'\t'<<Mul(A,B)<<endl; } Function Prototype contains only data types But may contain identifiers.

  23. Scope of Variables (1) Global variables: - Those variables that are declared before the main function. - These are visible from any point of the code, inside and outside any function. (2) Local variables: - These are declared inside a block or a function. - The scope of local variables is limited to the same nesting level in which they are declared.

  24. Example of Local and Global Variables // File: global.cpp #include <iostream.h> int x = 7 ; // global variables int fun1 (int ); // function prototype void main ( ) { int z ; // local variable in main cout << “The global variable: “ << x ; z = fun1 ( 5 ) ; // calling add function cout << “ The result is “ << z << endl ; } int fun1 ( int a ) { int r ; // local variable in fun1 r = a * a * a ; return r ; }

  25. Functions and Passing Parameters The mechanisms of passing parameters: (1) Call by value: - During the function call, the value of the argument is found and passed to the function. - Any modification inside the function does not affect the argument. (2) Call by reference: - During the function call, the address of the variable is passed to the function. - Any modification made on the parameter inside the function will have effect in the passed variable outside it.

  26. Difference between Function Definitions forCall by Value and Call by Reference • For call by value, we declare the arguments of the function as usual. Example: int func1 ( int , int ); // function prototype • For call by reference, the type of the argument is followed by the symbol (&) to specify that the variable has to be passed by reference. Example: void func2 ( int & , int & ); // function prototype

  27. Call by value When calling, the value of actual parameter will be copied to the formal parameter. #include <iostream.h> void Increment(int); void main() { int A = 10; Increment(A); cout<<A<<endl; } void Increment(int X) { ++X; }

  28. Call By reference When calling, the reference formal parameter will be an alternative name to the actual parameter. #include <iostream.h> void Increment(int&); void main() { int A = 10; Increment(A); cout<<A<<endl; } void Increment(int &X) { ++X; }

  29. Call By reference When calling, the pointer formal parameter will points to the actual parameter. #include <iostream.h> void Increment(int*); void main() { int A = 10; Increment(&A); cout<<A<<endl; } void Increment(int *X) { ++*X; }

  30. Example 5: Call by Value // File: calls1.cpp #include <iostream.h> // function prototype: the arguments to be passed by value int add (int , int ); void main ( ) { int x, y , z ; // local variables in main cout << “ Enter two integers: “ ; cin >> x >> y ; cout << “ x = “ << x << “ y = “ << y << endl; z = add ( x , y ) ; // calling add function cout << “ The result is “ << z ; cout <<“After call “<< “ x = “ << x << “ y = “ << y << endl; } int add ( int a , int b ) { return a + b ; }

  31. Execution of Example 5 • The user will be prompted to enter two integers. • The user enters, for example, 10 and 20 that are saved in x and y respectively. • When function add is called, the value of x and y are passed to the function. • The function add takes the values 10 and 20 and links them to a and b respectively. • The function will return the result which is 30. The output: Enter two integers: 10 20 x = 10 y = 20 The result is 30 After call x = 10 y = 20

  32. Example 6: Call by Reference // File: calls2.cpp #include <iostream.h> // function prototype: the arguments to be passed by reference void duplicate (int & , int & , int & ); void main ( ) { int x, y , z ; // local variables in main cout << “ Enter three integers: “ ; cin >> x >> y >> z ; cout << “ Before call: “ << “ x = “ << x << “ y = “ << y << “ z = “ << z <<endl; duplicate ( x , y , z ) ; // calling duplicate function cout <<“ After call: << “ x = “ << x << “ y = “ << y << “ z = “ << z <<endl; } void duplicate ( int & a , int & b , int & c ) { a *= 2 ; b *= 2 ; c *= 2 ; }

  33. Execution of Example 6 • The user will be prompted to enter three integers. • The user enters, for example, 10, 20, and 30 that are saved in x, y, and z respectively. • When function duplicate is called, the addresses of x, y, and z are passed to the function. • The addresses of x, y, and z are linked to the parameters of the function a, b, and c. The function will duplicate each parameter and save the result in the same parameter. Thus, a becomes 20 hence x becomes 20 also b becomes 40 hence x becomes 40 also c becomes 60 hence x becomes 60 also • After the call we see that the values of x, y, and z are changed. The output: Enter three integers: 10 20 30 Before call: x = 10 y = 20 z = 30 After call: x = 20 y = 40 z = 60

  34. Recursion Function call itself #include <iostream.h> int Fact (int N) { if (N<=1) return 1; else return N * Fact(N-1); } void main() { cout<<Fact(5)<<endl; }

  35. Example #include <iostream.h> int Zap (int N) { int Z; if (N<=1) Z=1; else Z= Zap(N-1) + Zap(N-3); return Z; } void main() { cout<<Zap(5)<<endl; }

  36. Array as parameter -Array name is pointer (call by reference) #include <iostream.h> void Increment (int a[]) { for (int i=0; i<5; i++) a[i] += 10; } void main() { int b[5] = {10,20,30,40,50}; Increment(b); for(int i=0; i<5; i++) cout<<b[i]<<'\t'; cout<<endl; }

  37. Array as parameter -Array element (call by value) #include <iostream.h> void Increment (int a) { ++a; } void main() { int b[5] = {10,20,30,40,50}; Increment(b[1]); cout<<b[1]<<endl; }

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