基本增量

Question

i know this is a very basic question BUT.

I understand the concept behind. n++, ++n, n--, --n. HOWEVER

public static void main(String[] args){

    int count = 1;
    for(int i =1;i<=10;++i){

    count = count * i;
    System.out.print(count);
    }
}

So it will print: 1 2 3 4 5 6 7 8 9 10.

My Question is. Why if i is incremented as ++i isnt i then treated as 2, instead of 1. Inst the point of ++i, to increment i before it's manipulated by another operation?

Answer 1

Is the point of ++i, to increment i before it's manipulated by another operation?

The difference between ++i and i++ only matters when it's used as part of a bigger expression, eg

int j = ++i; // Increment then use the new value for the assignment
int k = i++; // Increment, but use the old value for the assignment

In this case the operation occurs at the end of each iteration of the loop, on its own . So your loop is equivalent to:

int count = 1;
// Introduce a new scope for i, just like the for loop does
{
    // Declaration and initialization
    int i = 1;
    // Condition
    while (i <= 10) {
        count = count * i;
        System.out.print(count);

        // Now comes the final expression in the for loop "header"
        ++i;
    }
}

Now changing ++i to i++ at the end there isn't going to make a difference at all - the value of the expression isn't used for anything.

Answer 2

The increment isn't called until after the first iteration of the for loop.

While it's true that

j = i++;
k = ++i;

return different results, think of the ++i in this context as a standalone line called at the end of every for loop.

Answer 3

You want to use i++ which is a post increment. ++i is called a preincrement and the difference is precisely as you have pointed out.

Answer 4

In this case ++i happens at the end of the loop, it increments and then checks if the new value still meets the termination condition.

Also, won't the output be:

count   i  
1   *   1 = 1
1   *   2 = 2  
2   *   3 = 6   
6   *   4 = 24  

etc.

Answer 5

The for loop you wrote is same as:

i = 1;
while(i<=10) {
  count = count * i;
  System.out.print(count);
  i = i + 1;
}

So that's why!

Answer 6

For i = 0 and While i < 1= 10, print i, and then pre-increment i. (++i/i++ doesn't make a difference here).

Here try this though:

 int i=1; while(i <= 10) System.out.print(++i); i = 1; while (i <= 10) System.out.print(i++); 

Answer 7

As an addition to the other answers, the historical reason for preferring for(int i=1;i<=10;++i) over for(int i=1;i<=10;i++) is that ++i does not need to store the old value of i in an extra variable. Thus, ++i is faster than i++ , though the speed improvement is negligible. On modern compilers this speed improvement is done as an optimization, so the two pieces yield the same compiler output. However, since ++i is always as fast or faster (eg, on old C++ compilers) than i++ , many experienced programs always use ++i within loops.

As other answers have stated, both pieces of code are functionally equivalent (in the case of a for loop).