Sizeof structure in c

// (typical 32 bit machine)
 
// char         1 byte
// short int    2 bytes
// int          4 bytes
// double       8 bytes
 
// structure A
typedef struct structa
{
   char        c;
   short int   s;
} structa_t;
 
// structure B
typedef struct structb
{
   short int   s;
   char        c;
   int         i;
} structb_t;
 
// structure C
typedef struct structc
{
   char        c;
   double      d;
   int         s;
} structc_t;
 
// structure D
typedef struct structd
{
   double      d;
   int         s;
   char        c;
} structd_t;
 
int main()
{
   printf("sizeof(structa_t) = %d\n", sizeof(structa_t));
   printf("sizeof(structb_t) = %d\n", sizeof(structb_t));
   printf("sizeof(structc_t) = %d\n", sizeof(structc_t));
   printf("sizeof(structd_t) = %d\n", sizeof(structd_t));
 
   return 0;
}

What should be the o/p and explain it..

how can we prevent this erroneous behavior.