for loop

[hisoka]

the second statement in for loop tells how many times the loop will execute a piece of code :

 

var a = new Array("10","2");for(i=0 ; i<a.length ; i++){a=a+i;}

here in script the code is excuted endlessly although the second statement of the for loop is i<a.length . the length of the array is 2 so i<2 should loop one time . I do not understand why it loops endlessly???

 

 

Statement 2

Often statement 2 is used to evaluate the condition of the initial variable.

This is not always the case, JavaScript doesn't care. Statement 2 is also optional.

If statement 2 returns true, the loop will start over again, if it returns false, the loop will end.

 

 

what does this means :"If statement 2 returns true, the loop will start over again, if it returns false, the loop will end"??

 

 

[Jonathanks]

The first problem has the loop body reassign the variable 'a' to a number. Given it's initial value of a.length as 2, and the initial value of 'i' as 0, 'a' will always be greater since the value of i is continuously added to it. So the loop never ends.

[davej]

1. Don't use the Array() constructor. Instead declare an array with square brackets like this...

var a = ["10","2"];

2. If you have declared an array then use only legitimate operations on it. In your code above the statement a=a+1 makes no sense. See...

 

http://www.w3schools.com/jsref/jsref_obj_array.asp

 

3. If you have a for for-loop such as...

for(i=0 ; i<x ; i++){}

...then you would normally avoid changing the value of i or x inside that loop.

[hisoka]

The first problem has the loop body reassign the variable 'a' to a number. Given it's initial value of a.length as 2, and the initial value of 'i' as 0, 'a' will always be greater since the value of i is continuously added to it. So the loop never ends.

 

Thank you . However the loop looped endlessly not because of the because of this i<a.length but because of this

 

a=a+i; this is wrong and as a consequence of this error the loop looped endlessly

 

it must be like that

 

a=a[i+1] ;a=a[i+2] until 4 // this to change the position of the element in the array

 

a=a+1; until 1000000000000.... // this to add the first element of the array to the any number you want

 

 

a=a+i; it works too and is true

 

var a = ["10","2"]; this was an error : I do not use a debugger . I debug from my brain . So that it is sometime , difficult to notice such errors

 

thank you very much for the link and keep correcting me .

Edited February 22, 2015 by hisoka

[Ingolme]

Your problem is that a is an array. You cannot add a number to an array

 

When you write a = a + i, what are you expecting it to do?

 

What's happening in your script is that it casts the array to a string "10,2" and then concatenates i, resulting in "10,20". On the second iteration, a.length is now the length of the string, which is 5. Now a = a + i results in the string "10,201" which has length 6. On the third iteration a becomes "10,2012", a string with length 7. And this continues on and on, because a.length keeps getting bigger and i never catches up with it.

[hisoka]

yes , the error , as you wrote , was produced because I tried to add an array to a number