What is Global Variable and Scope in C Programming ?

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Global Variable : 

• Global Variable is Variable that is Globally available.
• Scope of Global variable is throughout the program [ i.e in all functions including main() ]
• Global variable is also visible inside function , provided that it should not be re-declared with same name inside function because ... "High Priority is given to Local Variable than Global"
• Global variable can be accessed from any function.

#include<stdio.h>
int var=10;
void message();
void main()
{
int var=20;
  {
  int var = 30;
  printf("%d ",var); 
  }
printf("%d ",var);
message();   
}
void message()
{
printf("%d ",var);   
}

Output :

30 20 10

• Inside message() 'var' is not declared so global version of 'var' is used , so 10 will be printed.

{
  int var = 30;
  printf("%d ",var); 
  }

• Here variable is re-declared inside block , so Local version is used and 30 will be printed.

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In Short -

1. For Inner Block variables declared in Outer Block acts as "Global Variable".
2. If block contain undefined variable then -
• It checks occurrence of that variable in outer block .
• If it is also undefined in outer block then global version is used .
• If it also undeclared globally then its extern definition is checked if not found then it throws error.
  

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Tags / Keywords : | global scope, global variable

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