#define DIAGONAL(xi,yi,xs,ys) (xs)-(xi)>=0 && (ys)-(yi)>=0?\
				sqrt(((xs)-(xi))*((xs)-(xi))+((ys)-(yi))*((ys)-(yi))):\
				0

----------- APLICADA ------------

#include <stdio.h>
#include <math.h>
#define DELTA 0
#define DIAGONAL(xi,yi,xs,ys) (xs)-(xi)>=0 && (ys)-(yi)>=0?\
				sqrt(((xs)-(xi))*((xs)-(xi))+((ys)-(yi))*((ys)-(yi))):\
				0

int main()
{
    int x1,y1,x2,y2;

    x1 = 2;
    y1 = 1;
    x2 = 1;
    y2 = 2;

    printf("La distancia de la punta (%d,%d) hasta la punta (%d,%d) es %g\n", x1,y1,x2+DELTA,y2+DELTA, DIAGONAL(x1,y1,x2+DELTA,y2+DELTA));

    return 0;
}