Change all the int type to another type using #define for large program

Question

I want to change all my int type in my program to support arbitrary position integer. I chose to use GMP.

I am thinking about is it possible to do a #define to replace all int to mpz_class.

I start by a small program

#include <iostream>
#define int long long int
using namespace std;

int main(){
    // .... code
}

The compiler is already complaining about main have to return an int type.

Is it possible to add exception to #define? or this is a really bad idea to do so?

Answer 1

Redefining a keyword is prohibited iff you include any standard headers. Here, you included <iostream> so your program is ill-formed.

Otherwise, knock yourself out! Wait, no, don't, because this would still be really silly.

Instead, refactor your code to use some new type called, say, my_integer (but with a much better name):

typedef int my_integer;

Then, when you want to change from int to mpz_class, you just change the definition of my_integer:

typedef mpz_class my_integer;

Answer 2

use main without int like this:

#include <iostream>
#define int long long int
using namespace std;

main(){
    // .... code
}

Answer 3

The simple answer: although technically possible you are not allowed to #define any of the reserved identifiers.