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From: Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups: comp.lang.javascript
Subject: Re: Bignumb addition function, suggestion improvements.
Date: Sat, 14 Mar 2015 19:39:57 +0000
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jonas.thornvall@gmail.com writes:

> Den lördag 14 mars 2015 kl. 14:41:35 UTC+1 skrev Ben Bacarisse:
>> jonas.thornvall@gmail.com writes:
>> 
>> > I just wrote a big numb addition function this morning, it is a bit
>> > silly and naive, not pure string not pure integer. I think it is
>> > correct, but i may have missed leading last digit.
>> 
>> Yes, you do miss the leading digit in some cases.  And it's only for
>> positive numbers.
>> 
>> > Suggestions to write it shorter and more clear, but keeping the naive
>> > approach appreciated.
>> >
>> > <SCRIPT LANGUAGE="Javascript">
>> >
>> > function naiveAdd(strOne,strTwo) {
>> > if (strOne.length>=strTwo.length) {length=strOne.length;} else
>> > {length=strTwo.length;}
>> > oneS = strOne.split("").reverse().join("");
>> > twoS = strTwo.split("").reverse().join("");
>> 
>> I would avoid this reversing operation.  It's not needed since you can
>> get the charCodeAt any index value you like.
>> 
>> > out="";
>> > remainder=0;
>> 
>> Use var.
>> 
>> > for (i=0;i<length;i++){
>> >          one=oneS.charAt(i);
>> >          two=twoS.charAt(i);
>> >          one=parseInt(one);
>> >          two=parseInt(two);
>> >          if (isNaN(one)) one = 0;
>> >          if (isNaN(two)) two = 0;
>> >          sum=one+two+remainder;
>> >          if (sum>=10) { sum=sum-10; remainder=1;} else {remainder=0;}
>> >          out=sum+out;
>> >     }
>> 
>> There's a bit of duplication here and a bug: you forget that the carry
>> (the usual name for your 'remainder') can be set at the end of the loop.
>> 
>> > document.write("Sum = ",out,"<BR>");
>> > }
>> >
>> > strOne="9003";
>> > strTwo="13039";
>> > naiveAdd(strOne,strTwo);
>> >
>> > </SCRIPT>
>> 
>> String.prototype.digitValueAt = function (pos) {
>>     var d = this.charCodeAt(pos);
>>     return isNaN(d) ? 0 : d - 48;
>> }
>
> I do not get ? 0 : d - 48;

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator

The 48 is "0".charCodeAt(0) which would be have been more self-documenting.

>  
>> function naiveAddX(strOne, strTwo) {
>>     var i1 = strOne.length, i2 = strTwo.length, result = "", carry = 0;
>>     while (i1 > 0 || i2 > 0 || carry > 0) {
>>         var dsum = strOne.digitValueAt(--i1) + strTwo.digitValueAt(--i2) + carry;
>
> What is the -- before i1 and i2?

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Decrement_(--)

<snip>
> I was thinking that adding to negative numbers basicly a subtranction
> -7+4=4-7, mult and div go before add and subtraction. So if i
> implement them and powers with a parser. Will the lack of add to
> negative numbers mess up things or can i use subtraction instead?

I don't follow.

-- 
Ben.