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If int i is not initialized then both expression ( assignment to a = (++i) ; and a = (i++) ) are wrong . Compiler Will produce an error related to initialization of integer i.

i++ increments the variable but returns its value before the increment.
++i increments the variable and returns a reference to the variable.

the = operator needs a L-value on the left side to be able to assign the value of a to i. the first statement does not return an L-value, while the second statement does (return variable i).

sup i=10, a=3;
->: ++i = a
-> : (i=i+1)=a //highest priority operator ++ other than = ,because first execute the left side statement
-> : i=11=a //here variable 'a' require left value.so,the compiler produced error "L Value required"
*This is same as post and pre increment

sup i=10, a=3;
->: ++i = a
-> : (i=i+1)=a //highest priority operator ++ other than = ,because first execute the left side statement
-> : i=11=a //here variable 'a' require left value.so,the compiler produced error "L Value required"
*This is same as post and pre increment

(++i) = a; // correct, the value of i increases and i is used as a variable.
(i++) = a; // incorrect, it tries to assign values to (i++), which is an operation, not a variable.

(++i) = a is correct, and (i++) = a is wrong.

If you use C++ and operator overload, you will know why: (++i) returns a l-value (like variable), while (i++) returns r-value, which cannot be assigned a value.

(++i)=a is correct
i++=a is incorrect
as ++i can be used as L-value
any pre-increement or pre decreement can be used as L-value
but post-increement cannot be used!

None of them are correct!
Rule :
When executing "x=y", 'x' should be assignable(for example, address where you store)

reason :
(++i) increments value of i and gives you after increment "value of 'i'"
(i++) gives you "value of i" and then increments 'i'.
So in the given problem, (++i) or (i++) always gives you "value" either before increment or after increment, to which you cannot "asssign some other value directly.

gcc gave me "error: lvalue required as left operand of assignment" for both

If you read the C or C++ standard, both would be wrong.

A compiler is more likely to accept ++i, but you should not code this way as it is not strictly allowed in the standards.

main.c:8:8: error: lvalue required as left operand of assignment
++i = a;
^
main.c:9:8: error: lvalue required as left operand of assignment
i++ = a;
^

Both are wrong. We need an lvalue.

i think both of them are wrong.because left hand side i cant use the increment operator

both are correct syntax wise(if they are initialized). post increment require another location to hold incremented value when compared to pre increment. So I will prefer pre-increment

What exactly are you looking for, that is the question?

both the lines are correct provide some initial value for i... here i++ is a post increment operator where value is assigned first and then incremented.whereas ++i is a pre increment operator where value is incremented and then assigned.

Am i wrong?
I have tried this code with MinGW,
++i=a ----> right
i++=a ----> compiler error

no matter i and a instantiated or not!