Engineering Problem Solving with C++, Second edition, J. Ingber 1 Engineering Problem Solving with C++, Etter/Ingber Chapter 5 Parameter Passing 11/06/13

PARAMETER PASSING pass by value pass by reference storage class and scope Engineering Problem Solving with C++, Second edition, J. Ingber 2

Parameter Passing  C++ supports two forms of parameter passing: –Pass by value. –Pass by reference. Engineering Problem Solving with C++, Second edition, J. Ingber 3

Parameter Passing  C++ supports two forms of parameter passing: –Pass by value. –Pass by reference. Engineering Problem Solving with C++, Second edition, J. Ingber 4

5 Parameter Passing - pass by value –Pass by value is the default in C++ (except when passing arrays as arguments to functions). –The formal parameter receives the value of the argument. –Changes to the formal parameter do not affect the argument.

Engineering Problem Solving with C++, Second edition, J. Ingber 6 //Function Definition int fact(int num)//4 { int nfact = 1;//5 while(num>1) { nfact = nfact*num; num--; } return(nfact);//6 } //end fact int main() { int n, factorial;//1 cin >> n; //2 if(n>=0) { factorial = fact(n);//3 cout << n <<"! is " << factorial << endl;//7 }//end if return 0; }//end main

Engineering Problem Solving with C++, Second edition, J. Ingber 7 Parameter Passing - pass by reference  Pass by reference allows modification of a function argument.  Must append an & to the parameter data type in both the function prototype and function header void getDate(int& day, int& mo, int& year)  Formal parameter receives the address of the argument.  Any changes to the formal parameter directly change the value of the argument.

Pass-By-Reference Example  scale.cpp

Engineering Problem Solving with C++, Second edition, J. Ingber 9 Example - pass by reference #include using namespace std; //Function swap interchanges the values of two variables //function definition void swap(double& a, double& b)//function header { double temp;//local variable temp temp = a; a=b; b=temp; return;//optional return statement }//end swap

Engineering Problem Solving with C++, Second edition, J. Ingber 10 Another Example - pass by reference int main() { double x = 5, y = 10; swap(x,y);//function call; x y are arguments cout >> “x = “ << x << ‘,’ << “ y= “ << y << endl; return 0; } //end main Output?

Engineering Problem Solving with C++, Second edition, J. Ingber 11 Practice! - What is the output? #include using namespace std; void fun(int& a1, int& a2, int a3) {a1++; a2++; a3--; } int main() {int c1=1, c2=2, c3=3; cout << c1 << ‘,’ << c2 << ‘,’ << c3 << endl; fun(c1,c2,c3); cout << c1 << ‘,’ << c2 << ‘,’ << c3 << endl; fun(c3, c2, c1); cout << c1 << ‘,’ << c2 << ‘,’ << c3 << endl; return 0; }

Engineering Problem Solving with C++, Second edition, J. Ingber 12 Scope  Scope refers to the portion of the program in which it is valid to reference a function or a variable.  Block  A sequence of statements enclosed in {} that introduces a new scope

13 Scope  Local scope - a local variable is defined within a function or a block and can be accessed only within the function or block that defines it  Global scope - a global variable is defined outside the any function and can be accessed by any function within the program file.

14 Scope  Ch5/scope1.cpp - Global PI and local variables belonging to the functions  Ch5/scope2.cpp - Global variable referred to in main and other function.  Ch5/scope3.cpp - Local variable declared within an if block.

15 Questions  Use pass-by-______________ when a change in the argument is desired.  The_________ of a name is the portion of the program in which the name can be used.  A variable declared outside of any block is called a _________ variable.

Write a Midpoint Function Write a C++ function to find the midpoint of a line segment in a Cartesian plane, given the coordinates of the endpoints of the segment.

Write normalize( ) Write a C++ function to take the numerator and denominator of a fraction. It should normalize the fraction. Change the fraction so that the denominator is a positive number.