Des octets magiques ???

#include <ansi_c.h>
#include <userint.h>

typedef struct
{
    int    champ1;
    double champ2;
} t_struct;

int main(void)
{
    t_struct var1;
    unsigned int na, nb, ns, nsa, nsb;
    int      a=1;
    double   b=2.3;
    
    var1.champ1 = a;
    var1.champ2 = b;
    
    na = (unsigned int) sizeof(a);
    nb = (unsigned int) sizeof(b);
    ns = (unsigned int) sizeof(var1);
    nsa = (unsigned int) sizeof(var1.champ1);
    nsb = (unsigned int) sizeof(var1.champ2);
    
    printf("taille de a = %d octets\n",na);
    printf("taille de b = %d octets\n",nb);
    printf("taille de var1.champ1 (= a) = %d octets\n",nsa);
    printf("taille de var1.champ2 (= b) = %d octets\n",nsb);
    printf("taille de var1 = %d octets\n",ns);
    printf("D'ou viennent ces 4 octets ?!!!\n"); 
    MessagePopup ("", "OK");
}