Declaring the size of int, double, floats

[persianmess]

#include <iostream>
using namespace std;      
int main()
{
        int i;
	float  x, y, z;
	double d; 

        i = 15;
	d = 40;
	x = 25;
	y = 125;
	z = y/x;

        return 0;
}

Question to all .. I need to declare the size of my int, float(s), and the double listed above. How would I got about doing so?

For instance, my string: string str ("str");
I did it like: cout << "The size of my str is: " << str.size() << " characters." << endl;

Please help!