How to measure the size of int and short variable by memory allocating features?

I tried to test the length of int and short type in my computer (X86_64), so I wrote two pieces of codes as bellow: short:

short a;
scanf("%hd%hd",&a,&a+1);
printf("%hd",a+*(&a+1));

int:

int a;
scanf("%d%d",&a,&a+1);
printf("%d",a+*(&a+1));

Both work and output the right answer, but when I change to number 1 to 4, the first one works well while the second one show a Segmentation fault after input.
Some materials say that the lengths of short and int are all 16 bits in x86, I don't know the difference in x86_64, are they the same? In addition, what caused the Segmentation fault?

PS:I use gcc -Wall -O2 -o filename -lm to compile.

I have known what's wrong with my code after reading your comments and answers.
I guessed the address of a variable is like that in assembly language, so if I get an address and add it with the length of a variable I can get the address of the following viable. I use &a+4 first to test if the length of int is 4 BYTES, but there was a Segmentation fault while running, I changed 4 to 1 and get the correct value, I didn't understand why this worked? Now, I got it.
In the following code:

short a,b;
a = b = 1024;
cout << &a << endl << &b << endl;
cout << &a << endl << (&a) + 1;

An output of it is:

0xbfad153c  
0xbfad153e  
0xbfad153c  
0xbfad153e 

And

int a,b;
a = b = 1024;
cout << &a << endl << &b << endl;
cout << &a << endl << (&a) + 1;
return 0;

An Output is:

0xbfddb968  
0xbfddb96c  
0xbfddb968  
0xbfddb96c  

It shows that &a + 1 here plus the value of the size of int a but not the literal const value of 1
So I just want to use the feature of memory allocating to measure the size of int and short, not sizeof function.
Thanks for your answers and comments, even though they are not what I want to get.