分号在for循环中如何工作？

Question

I am writing a function that raises a value to another value without using the exponent operator. I understand the syntax of these kinds of loops as being that initialised values go before the first semicolon, a condition goes between the first and the second semicolon, and after the second semicolon is the looping operations.

I am confused because I think this code should be broken, but it appears to return the correct value. When I put result *= base after count++ inside the parenthesis, then the code does not return the correct value. Why is this?

 //Power function function power(base, exponent) { var result = 1 var count = 0 for (; count < exponent; count++) result *= base return result; } print(power(5, 2)); 

Answer 1

The blank ; just acts as a placeholder in this case. Because you declared count = 0 above this for loop, this ; is just there so that declaration isn't overwritten:

 var count = 0; for(/*var count=0*/; count < 4; count++){ document.write(count); } 

PS I commented out var count = 0 because that is essentially what the code is representing (because you called that earlier).

Answer 2

It is possible to do what you want in javascript. I think the only problem is that you didn't use brackets. This will work.

 //Power function function power(base, exponent){ var result = 1; var count = 0; for (; count < exponent; count++, result *= base) {} return result; } document.write(power(5, 2)); //returns 25 

But this won't because even if you don't indent return, it will be executed in the for loop and return during the first iteration. I ran in this issue when I tried your code snipplet so I think it is your issue :

 //Power function function power(base, exponent){ var result = 1; var count = 0; for (; count < exponent; count++, result *= base) //notice the missing brackets return result; } document.write(power(5, 2)); //returns 25