谁能告诉我 for 循环中发生了什么

Question

Here is the code that computes 2 10 , using for loop : How did the 1024 answer come?

var result = 1;
for ( var counter = 0; counter < 10; counter = counter + 1)
result = result * 2;
console . log ( result );
//  1024

Answer 1

Basically

1024 = 2 ¹⁰

(2 * 2 ... 10 times)

The for loop loops 10 times, each time result is multiplied by 2 (was 1 initially).

Indenting you code gives

var result = 1;

for ( var counter = 0; counter < 10; counter = counter + 1)
    result = result * 2;

console . log ( result );  // display result in console

Answer 2

Since you don't have a block ( {} ) around the for loop statements, only the first statement is in the loop ( result = result * 2; ), so it's multiplying the result with 2, 10 times, ie

result = 1 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2

and after that you are outputing that result ( 1024 ).

Answer 3

Your for loop only runs result = result * 2 .

Now, your result initial value is 1 . Then this will do the operation of result * 2 for 10 times which gives the result of 1024

2
4
8
16
32
64
128
256
512
1024

Answer 4

for (statement 1; statement 2; statement 3) {
    code block to be executed
}

Statement 1 is executed before the loop (the code block) starts.

Statement 2 defines the condition for running the loop (the code block).

Statement 3 is executed each time after the loop (the code block) has been executed.

In your case, this loop runs 10 times. In your "statement 1", you assign counter to 0.Then, you define the condition, which is that the for loop will run until counter is = or > 10 (so until the condition isn't met). On "statement 3" you are just adding one to counter at the end of every loop.

Therefore, you are multiplying variable "result" (which is assigned a value of 1) times 2, 10 times . After that, the console.log just prints the result variable.

//2^10 = 1024

hope this helps, here's a link to for loop syntax: http://www.w3schools.com/js/js_loop_for.asp