Comma expression, comma

Comma expression, comma

What are the running results of this program? 0? See the following
 
Yes, it's not 0, it's 1!
You may wonder why 1 is not 0? We will not talk about this for the moment.
P = a [0] = & a [0] [0] Everyone knows this, so p [0] represents * (p + 0) that is, * (& a [0] [0]). From the inverse operation between * and &, p [0] is a [0] [0].
So there is a problem! What is a [0] [0?
Many may think that a [0] [0] is 0, but it is not. In this case
A [0] [0] is indeed 0. You can observe the slight differences between the codes at both ends. That is, the difference between () and.
When initializing a two-dimensional array, we use {} to aggregate the elements of the same row. {} is used to divide the region, and each {} is an element of a row, in addition, {} is not an operator. () Is a priority-level operator, but it cannot divide each line of elements when initializing a two-dimensional array. That is to say...int a [3] [2] = {(0), (1), (2)}; and. int a [3] [2] = {0, 1, 2}; is completely equivalent ......
But... what is the comma !?
Speaking of this, we have to mention a very easy to ignore operator. It is called the comma operator, also known as the order evaluation operator. Among all operators, the priority is the lowest (Level 15th ). An expression composed of commas (,) is also called a comma (,), in the form
Expression 1, expression 2 ,......, Expression n
When used, the values of Expressions 1, 2, 3,..., and n are obtained in sequence, and the value of expression n is taken as the value of the entire comma expression.

After reading this, you will surely understand why Exercise 4 has a result of 1 instead of 0. In fact
It can also be written as int a [3] [2] = {1, 3, 5 };
Only values 1, 3, 5 are assigned to a [0] [0], a [0] [1], and a [1] [0], and the values of other elements are 0. So the output value of a [0] [0] is of course 1 ~

An additional question is provided:

Main () {int x, y, z; x = y = 1; z = x ++, y ++, ++ y; printf ("% d, % d, % d \ n ", x, y, z );

}

The output result of the above program is:

The correct answer should be 2, 3, 1