Analysis of the difference between i++ and ++i in PHP and _php example of efficiency

First look at the basic difference:

i++: First use the current value of I in the expression where I is, then let I add 1

++i: Let I add 1 first, and then use the new value of I in the expression where I is

See some video tutorials inside write for loop is written ++i instead of i++, Internet search for a while, the original efficiency problem

++i is equivalent to the following code

i + 1; 

i++ is equivalent to the following code

j = i; 
i + 1; 
Return J;

Of course, if the compiler will optimize these differences, then the efficiency is all the same.

To give you a detailed talk about the difference between ++i and i++

1, the use of ++i (A=++i, i=2 as an example)

First add the I value by 1 (that is, i=i+1), and then assign the variable a (that is, a=i),

The final a value is equal to 3, and the I value equals 3.

So a=++i is equivalent to i=i+1, a=i

2, the use of i++ (a=i++, i=2 as an example)

First assigns the I value to the variable a (that is, a=i), and then the I value plus 1 (that is, i=i+1),

The final a value is equal to 2, and the I value equals 3.

So a=i++ is equivalent to A=i, i=i+1

3, ++i and i++

A=++i is equivalent to i++, a=i

a=i++ is equivalent to A=i, i++

4, ++i and i++ when used alone, the equivalent of i=i+1

If you assign a new variable, ++i first adds the I value to 1, and i++ first assigns I to the new variable.

The above is a small set to introduce PHP i++ and ++i of the difference and efficiency of all the narration, I hope to help you, if you have any questions please give me a message, small series will promptly reply to everyone. Here also thank you very much for the cloud Habitat Community website support!