How to find greatest of 2 numbers using functions without arguments?

CODE

How to find greatest of 2 numbers using functions without arguments?

//Write a program to find greatest of 2 numbers using functions without arguments..

int main()

{

    void gr();

    gr();

}

void gr()

{

    int a,b;

    printf("\n enter 2 numbers:");

    scanf("%d%d",&a,&b);

    if(a>b)

        printf("\n first number is greater");

    else if(b>a)

        printf("\n second number is greater");

    else

        printf("\n both are same");

}

Output:

enter 2 numbers:

87

54

 first number is greater.