Intro to Programming Week # 8 Functions II Lecture # 13 By: Saqib Rasheed

Parameters by value When arguments are passed by value, the called function creates a new variable of the same type and copies the argument’s value into it. Function cannot access the original variable in the calling program, only the copy it created. Passing arguments by value is useful when the function does not need to modify the original variable in the calling program. In fact, it offers insurance that the function cannot harm the original variable. Saqib Rasheed

Parameters by reference Passing arguments by reference uses a different mechanism. Instead of a value being passed to the function, a reference to the original variable, in the calling program, is passed. It’s actually pass the memory address of the variable that is passed An important advantage of passing by reference is that the function can access the actual variables in the calling program. Among other benefits, this provides a mechanism for passing more than one value from the function back to the calling program.

Example void foo(int &y) { cout << "y = " << y ; y = 6; cout << "y = " << y; } // y is destroyed here void foo(int &y) ; int main() {     int x = 5;     cout << "x = " << x ;     foo(x);     return 0; } Saqib Rasheed

Passing By Value Versus Passing By Reference int &x; The parameter x is a local reference. It is a copy for the argument. It can change the argument. The argument passed by reference must be a variable. The argument is read-write. Passing By Value int x; The parameter x is a local variable. It is a duplicate of the argument. It cannot change the argument. The argument passed by value may be a constant, a variable, or an expression. The argument is read-only. Saqib Rasheed

Passing values by reference e.g void square(double &); void main() { double x; cout <<"\n main(), before calling "; cout<<"\nEnter the number to find square="; cin>>x; square(x); cout <<"\n main(), after calling square(), x = " << x<<endl; } void square(double &x) x=x*x; Saqib Rasheed

Example Develop a program that swap the two values using function by reference i.e a = 22.2 b = 44.4 After swap a = 44.4 b = 22.2 Saqib Rasheed

Example(code) void swap(float ,float ); void main() { float a = 22.2,b = 44.4; cout << "a = " << a << ", b = " << b << endl; swap(a,b); } void swap(float x, float y) float temp = x; x = y; y = temp; Saqib Rasheed

Example(code) void swap(float&,float&); void main() { float a = 22.2,b = 44.4; cout << "a = " << a << ", b = " << b << endl; swap(a,b); } void swap(float& x, float& y) float temp = x; x = y; y = temp; Saqib Rasheed

Function Overloading int test() { } int test(int a){ } int test(double a){ } int test(int a, double b){ } All 4 functions mentioned above are overloaded function. It should be noticed that, the return type of all 4 functions is same,i.e, int. Overloaded function may or may not have different return type but it should have different argument Saqib Rasheed

Example void test(int); void test(float); void test(int, float); int main() { int a = 5; float b = 5.5; test(a); test(b); test(a, b); return 0; } void test(int var) { cout<<"Integer number: "<<var; } void test(float var){ cout<<"Float number: "<<varl; void test(int var1, float var2) { cout<<"Integer number: "<<var1; cout<<" And float number:"<<var2; Saqib Rasheed

Overloading the max() Function #include<iostream.h> int max(int,int); int max(int,int,int) ; int main() { int x,y,z; cout<<"Enter x ="; cin>>x; cout<<"Enter y ="; cin>>y; cout<<"Enter z ="; cin>>z; } Saqib Rasheed

Overloading the max() Function cout << "Largest Among Two = "<<max(x,y) << "\nLargest Among Three =" << max(x,y,z); cout<<endl; int max(int x,int y) { // returns the maximum of the two given integers: return (x > y ? x : y); } int max(int x,int y, int z) { // returns the maximum of the three given integers: int m = (x > y ? x : y); // m = max(x,y) return (z > m ? z : m); Saqib Rasheed