Global Variables in C

A global variables are declared outside all functions, usually at the top of the program.

• Global variables have a program-wide scope which means can be accessed and modified by any function in the program. Note that local variables are restricted to a single function.
• If not explicitly initialized, global variables are automatically set to 0.
• They exist in memory for the entire runtime of the program.

#include <stdio.h>

// global variables
int a, b;

void add()
{

    // we are adding values of global a and b i.e. 10+15
    printf("%d", a + b);
}

int main()
{
    // we are now updating the values of global variables as you can see we dont need to redeclare a and b
    // again
    a = 10;
    b = 15;
    add();
    return 0;
}

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Advantages of Global Variable

• Global variables can be accessed by all the functions present in the program.
• Only a one-time declaration is required.
• Global variables are very useful if all the functions are accessing the same data.

Disadvantages of Global Variable

• The value of a global variable can be changed accidentally as it can be used by any function in the program.
• If we use a large number of global variables, then there is a high chance of error generation in the program.
• It is generally recommended to avoid global variables unless necessary.