Question

What are the issues that may arise if variables are declared globally, rather than being declared locally? State and discuss a C++ code example.
Are there any rules that should be followed in determining the scope of a variable? If so, what are they?​

Answer 1

Issues with global variables:

Issues With Global Variables:

• Global variables are memory locations that are directly visible to an entire software system.
• The problem associated with global variables is that different parts of the software are coupled in ways that increase complexity and lead to subtle bugs.
• Globals have system-wide visibility and are not same as static variables. Globals also increase the risk of data concurrency problems. Pointers to globals are the most evil things.
• In its plainest form , a global variable is accessed directly by name rather than being passed as a parameter.

Following is the c++ example:

#include <iostream>

// variables declared outside of a block are global variables

int x; // global variable x

const int y; //global variable y

void seeThem()

{

   // global variables can be seen and used everywhere in program

   x =3;

   std::cout << y << endl;

}

int main()

{

   seeThem();

   // global variables can be seen and used everywhere in    program

   x = 5;

   std::cout << y << endl;

  

   return 0;

}

Rules that should be followed in determining the scope of a variable:

Rule 1:

The scope of an entity is the program or function

in which it is declared.

There is a direct consequence of Scope Rule 1. Since an entity declared in a function has a scope of that function, this entity cannot be seen from outside of the function.

Rule 2:

A global entity is visible to all contained functions,

including the function in which that entity is declared.

Rule 3:

An entity declared in the scope of another entity is always

a different entity even if their names are identical.