What does "for" does in this code?

Question

function a(){
var pm = ""
var str = "HI";
for(var i = 0; i<str.length; i++){
if(str[i] == "H"){
pm += "h"
}
else if(str[i] == "I"){
pm += "i"
}
}
document.write(pm)
}
a()

Answer 1

No, that's not what I meant, okay let's review the code ...

var count = 0

// first "if" 'count' value is still zero ...

if(str[count++] == "H")
// this is true, because str[0] == "H"

// the second "if" sees that 'count' value is now 1 (incremented) so when we check ...

if(str[count++] == "I")

// this is true, because str[1] == "I"

BUT if we use else...if ...
count = 0

if(str[count++] == "H") {
// this block is executed, because str[0] == "H"
}
else if(str[count++] == "I") {
// the else..if block is not executed, because str[0] not equals "I" ...
}

I hope it's clear enough, come ask again if you still unsure ...

Answer 2

The first code uses loop to iterate the <str> and concatenate a lowercase "H" or "I" into <pm> when one was found in <str>.

The second code only adds "h" to pm variable because the part that checks for "I" is in the else..if block. If you want the same output, change it to

if(str[count++] == "I")

This will check the second character in <str> and adds "i" into <pm>.

Hth, cmiiw

Answer 3

Sina it was because the else...if block is supposed to be executed when the "if" part sees that str[count++] value does not equal to "H", when the "if" part is evaluated, the 'count' variable value was still zero (due to post increment operator), and the character at index zero was "H".

The second "if" however, sees that 'count' variable value has been incremented to 1, and the character at index 1 is "I", so the evaluation yields true, then the "i" character is added to 'pm' variable.

Hth, cmiiw

Answer 4

Why when I change it to "if" it works but when it's "else if" it doesn't work

Answer 5

you mean when we use if the countstart from zero agin yes??

Answer 6

and what is diffrent between this and that

var count = 0;
function a(){
var str = "HI";
var pm = "";
if(str[count++] == "H"){
pm += "h"
}
else if(str[count++] == "I"){
pm += "i"
}
document.write(pm)
}
setInterval(a)

Answer 7

Ok underestood thanks a lot