Global variables are defined outside of all the functions, usually on top of the program. The global variables will hold their value throughout the lifetime 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.
Example
#include <iostream>
using namespace std;
// Global variable declaration:
int g;
int main () {
// Local variable declaration:
int a, b;
a = 10;
b = 20;
g = a + b;
cout << g;
return 0;
}Output
This will give the output −
30