c# - Incrementing and decreasing i is not working properly -

the following 2 lines of code not returning same value. reason that?

int i;  = 1; = + i++; //returns 2, expecting 3 

and

i = 1; = i++ + i; //returns 3 

semantically, should same a + b = b + a right?

the same decreasing i:

i = 1; = - i--; //returns 0, expecting 1 

and

i = 1; = i-- - i; //returns 1, expecting -1 

what confuses me more usage of post increment operators:

i = 1; = + ++i; //returns 3 

and

i = 1; = ++i + i; //returns 4, expecting 3 

same again decreasing operator:

i = 1; = - --i; //returns 1 

and

i = 1; = --i - i; //returns 0, expecting -1 

last question:

how these 2 lines interpreted compiler?

i = i+++i; // + ++i or i++ + i? = i---i; // - --i or i-- - i? 

i = + i++; //returns 2, expecting 3 

know post increment. value used first , incremented. equivalent to

i = + i; = i+1; 

and pre-increment. value incremented first , used.

i = i++ + i; //returns 3 

is equivalent to

i = i+1; = + i; 

i = i+++i; // + ++i or i++ + i?

is interpretted

i = + 1; = + i;

and this

i = i---i; // - --i or i-- - i?

is interpretted as

i= i-1; = i-i;