Declaring a Global Variable Inside a Function

Using global variables in a function

You can use a global variable within other functions by declaring it as global within each function that assigns a value to it:

globvar = 0

def set_globvar_to_one():
    global globvar    # Needed to modify global copy of globvar
    globvar = 1

def print_globvar():
    print(globvar)     # No need for global declaration to read value of globvar

set_globvar_to_one()
print_globvar()       # Prints 1

Since it's unclear whether globvar = 1 is creating a local variable or changing a global variable, Python defaults to creating a local variable, and makes you explicitly choose the other behavior with the global keyword.

See other answers if you want to share a global variable across modules.

Creating global variables inside function - why does this work?

Afaik, variables declared inside a function are local variables (using var keyword or not).

Variables declared inside a function are local, but you are not declaring any variables. What you have is what's known as an "implicit global" and it only works in "sloppy mode".

From MDN:

Assigning a value to an undeclared variable implicitly creates it as a global variable (it becomes a property of the global object) when the assignment is executed.

In strict mode, your code produces an error:

"use strict";
function func1() {  x = 5;}
function func2() {  document.write(x);}
func1();func2();

Declaring a global variable inside a function

you have to define the global var in the second function as well..

// global scope
$ref_id = 1;

grabReferral($rid){
   global $ref_id;
   $ref_id = $rid;
}

someOtherFunction(){
    global $ref_id;
    sendValue($ref_id);
}

felix

How to declare a Global variable inside any function in 'C'?

You may want to use an array allocated into the heap by using malloc

#include<stdio.h>
int *a;
int main()
{
  int n;
  scanf("%d", &n);
  a = malloc(sizeof(*a) * n);
  if(a == NULL) {
      // malloc error
  }

  // use your array here

  free(a); // at the end of the program make sure to release the memory allocated before
}

How to declare global variable inside function?

You have two problems:

1. main is not a loop. It's a function.

2. Your function syntax is wrong. You need to have parentheses after the function name. Either of these are valid syntaxes for main:

    int main() {
    }
   
    int main(int argc, const char* argv[]) {
    }
   

Then, you can declare a local variable inside main like so:

int main() {
  int local_variable = 0;
}

or assign to a global variable like so:

int global_variable;

int main() {
  global_variable = 0;
}

initialize global variable in method

If you want to make some variable global then you would need to declare the variable outside the method. In java, you cannot declare static variables inside method (even if it is static) because inside method all variables are local variables that has no existence outside this method thats why they can't be static.

import java.util.*;

public class GlobalVariable{
    static int b;
    public static void main(String...args){
        GlobalVariable.compare(1);
        System.out.println(b);
    }

    static void compare(int a){
        Scanner sc = new Scanner(System.in);
        b = sc.nextInt();
    }
}

why can't I declare a global variable inside an exec string

You have to declare that you are using global ostr in the function to be able to print it. This piece of code outputs

def function():
   global ostr
   exec("global ostr; ostr = nstr")
   #global ostr; ostr = nstr
   print(ostr)
   lv='ostr' in globals()
   print(lv)
   ostr='asd'

worked

True

Edit: Just realised the exec actually works with global variables, if you re-run your code and print(ostr) in the global main you will see it was changed.

ostr = "didn't work"
nstr = "worked"
def function():
    #global ostr
    exec("global ostr; ostr = nstr")

function()
print(ostr)

worked

Edit#2: Either declare ostr as a global variable before modifying it, or assign it to another local variable.

ostr = "didn't work"
nstr = "worked"
def function():
    exec("global ostr; ostr = nstr")
    #global ostr; ostr = nstr
    print(ostr)
    lv='ostr' in globals()
    print(lv)
        
function()

worked

True

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