Loop values in variable using jquery

Question

yesterday I asked question which have been answered correctly. Now I want spend more time to understand that function which answered yesterday. In that function loop is adding value '7' in 'num' variable. I want to know how its adding value in 'num'.

var Arr = [ 'h78em', 'w145px', 'w13px' ]

function stringToNum(str){
  num = 0;
  for (i = 0; i < str.length; i++) 
    if (str[i] >= '0' && str[i] <= '9') 
      num = num * 10 + parseInt(str[i]);
  return num;
}

alert(stringToNum(Arr[0]));

here is fiddle

mdas rules apply you multiplied num by 10 first before adding the parse value, therefore 0 * 10 + 78 = 78 — ianace
– ianace, Commented Aug 31, 2012 at 6:15
if you remove *10 + parseInt(str[i]); and then alert num it will return 7, i want to know how it is 7 is passing to num variable — Jitender
– Jitender, Commented Aug 31, 2012 at 6:21

Prabhuram · Accepted Answer · 2012-08-31 06:24:28Z

2

In the given code, when the function is called, the if condition checks for each string in the passed value and when the variable is a number, the following code is executed

   if (str[i] >= '0' && str[i] <= '9') 
      num = num * 10 + parseInt(str[i]);

so in the given string, the first number occurs is 7. Since the value of num is initially zero the value of num will be,

 num=( 0 *10) + 7

so num=7 in the first occurence of the number. On the second occurence of a number, ie 8

the value of num will be,

  num=(7*10)+8

hence the value is 78

answered Aug 31, 2012 at 6:24

Prabhuram

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1 Comment

Jitender Over a year ago

Thanks a lot sir ji. You have very nice way to explain.

xdazz · Accepted Answer · 2012-08-31 06:24:49Z

1

The below function will be much simpler.

function stringToNum(str) {
  return +str.replace(/\D/g, '');
}

Update:

With your code:

init : num = 0
met 7: num = 0 * 10 + 7 -> num = 7
met 8: num = 7 * 10 + 8 -> num = 78

edited Aug 31, 2012 at 6:24

answered Aug 31, 2012 at 6:17

xdazz

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3 Comments

Jitender Over a year ago

i dont want new answer for the same, i just want understand this

xdazz Over a year ago

@amit What is the part you can't understand?

nbrooks Over a year ago

@amit It's much better to get rid of non-digits using regex than to iterate over the string parsing each digit individually (+1 @xdazz). It's cleaner, easier to understand at a glance, and should perform better (certainly as the string grows longer)

Maksim Vi. · Accepted Answer · 2012-08-31 06:26:34Z

1

1 iteration: num = 0; // h

2 iteration: num = 0 * 10 + 7; // 7

3 iteration: num = 7 * 10 + 8; // 8

4 iteration: num = 78; // e

5 iteration: num = 78; // m

answered Aug 31, 2012 at 6:26

Maksim Vi.

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