Address

• A variable may have different addresses at different times during execution
• A variable may have different addresses at different places in a program
• If two variable names can be used to access the same memory location, they are called aliases
• Aliases are created via pointers, reference variables, C and C++ unions
• Aliases are harmful to readability (program readers must remember all of them)
• Memory Address is called l-value.  ( l means left)
• Variables appear on the left of assignment statement.
• Same Name can be associated with different memory location.
• e.g.  a reference to sum in subprogram 1 is unrelated to reference to sum in subprogram 2.

#include <iostream>
using namespace std;

int temp = 5;
 
int passfun(int x);

int main(){
   int temp = 10;
   temp = passfun(temp);
   cout << "temp in main = " << temp << endl;
   return 0;
}
int passfun(int x){
   cout << "temp in subprogram = " << temp << endl;
   return x + temp;
}
• e.g. a recursively called subprogram has multiple versions of each locally declared variable, one for each activation.
• Python programs
• Static Scoping or Dynamic Scoping
• Aliases:    When more than one name is associated with a single memory location, the names are aliases.
• To create alias:
• FORTRAN use EQUIVALENCE
• Pascal, Ada use variant record structure
• C, C++ use union type
• Two pointer variables reference to the same memory location.
• Readability: Aliasing is a hindrance to readability because it allows a variable
to have its value changed by an assignment to a different variable
e.g.  If A & B are aliases, any change to A also change to B..
• Reusing storage: It is not so important now since computer memories are far larger now.
• Interface between subprograms:

e.g. In C++, use reference parameters to pass information.

#include <iostream>
using namespace std;
void getData(int &A, int &B);
int main()
{
   int num1, num2;
   getData(num1, num2);
   cout<<"The sum of "<<num1<<" and "<<num2<<" is "<<num1+num2<<endl;
      return 0;
}
void getData(int &A, int &B)
{
   cout<<"Please enter two numbers. \n";
   cin>>A>>B;
}