Question

How can I declare a global variable in Xcode and its data type should be integer and accessible by every class.

Answer 1

In some very special cases a truly global variable can simplify things. I don’t think you researched the problem exhaustively, but here is my answer anyway, a simple case:

// Globals.h
#ifndef Globals_h
#define Globals_h

extern NSInteger globalVariable;

#endif

// main.m 

NSInteger globalVariable;

int main(int argc, char *argv[])
{
   globalVariable = <# initial value #>;
    ...
}

// Prefix.pch

#ifdef __OBJC__
    #import 
    #import <Foundation/Foundation.h>
    #import "Globals.h"
#endif

Now, you can use globalVariable anywhere in your code, you don’t even need to include the header file.

Warning: things are slightly complex if you need thread safety or a different variable type.