What is a variable scope?


Scope of a variable

Scope refers to the visibility of the variable. Broadly speaking it means in which region or which piece of code have access to that variable. There are generally two scopes of variables
·        Inside a function or a block which is called local variables,
·        Outside of all functions which is called global variables.

Local Variables

Variables that are declared inside a function or block are local variables. They can be used only by statements that are inside that function or block of code. Local variables are not known to functions outside their own. Following is the example using local variables:
#include
using namespace std;

int main () {
   // Local variable declaration:
   int a, b;
   int c;

   // actual initialization
   a = 10;
   b = 20;
   c = a + b;

   cout << c;

   return 0;
}
Output
30
Global Variables
Global variables are defined outside of all the functions, usually on top of the program. The global variables will hold their value throughout the life-time of your program.
A global variable can be accessed by any function. That is, a global variable is available for use throughout your entire program after its declaration. Following is the example using global and local variables:
#include
using namespace std;

// Global variable declaration:
int g;

int main () {
   // Local variable declaration:
   int a, b;

   // actual initialization
   a = 10;
   b = 20;
   g = a + b;

   cout << g;

   return 0;
}
Output
30
A program can have same name for local and global variables but value of local variable inside a function will take preference. For example:
#include
using namespace std;

// Global variable declaration:
int g = 20;

int main () {
   // Local variable declaration:
   int g = 10;

   cout << g;

   return 0;
}
When the above code is compiled and executed, it produces the following result:
10


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