C Programming - Structures, Unions, Enums - Discussion

Hear we are not assign any value to.

Int i; how to compiler assign 515 value.

In the above question:

union a
{
int i;
char ch[2];
};

Here, memory is allocated for int i, i.e 2 bytes now.

u.ch[0]=3;
u.ch[1]=2;

They are stored in memory allocated for int i (as char are of 1 bytes) they are placed in each bytes of integer i, now when we print.

printf("%d, %d, %d\n", u.ch[0], u.ch[1], u.i);
return 0;

Then, first u.ch[0] is printed then u.ch[1] then u.i where u.ch[0] then u.ch[1] from right to left is stored in memory allocated for u.i is saved.

I understood how 515 is printed. I don't understand Why does doing u, i print that value?

I can't understand that. How 512 is came?

main()
{
union a{
int i;
char ch[2];
union a u;
u.ch[0]=3;
u.ch[1]=2;
here as we know the max size will be allocated is 2 bytes as size of character array is 2. Each value first represented in binary form and then stored in alloted memory space.This memory space again subdivided into two depending on no.of characters, as here two so(each having 8bits for storage).

So now according to binary display it is always from left to
right so the storing for characters will start from left which will be followed towards right consecutively.

Illustration:

2^15..........2^9 2^8 2^7 2^6...........2^1 2^0
| | | |
1 0 1 1
so u.ch[0]=3.
u.ch[1]=2.
u.i=2^9+2^1+2^0(summation of memory locations containing 1).
=512.

Thank you.

u.ch[0]=3;
u.ch[1]=2; for calculating (u.i) why we are taking 2 as first and 3 as second value?

I want to know how to write this code.

1st reduce the value of A by 1 then find sum A and B then incriment B by 1?

But Why ch[0] is right side of ch[1]. Means why it is Right to left?

@Ramkumar.

It depends if you print using %d then it will print the ASCII value of a and b or if you print using %c it will print actual character i.e a and b.

And if you print u.i it will print the 25185 (calculate as same process as above discuss).

u.ch[0]='a';

u.ch[1]='b';

Can anyone explain output for this definition instead of u.ch[0]=3;

u.ch[1]=2;?