Multiply large numbers

[tollar]

We have some problems to figure out how to multiply large numbers...
We are using strings with each large number in it..
the way we have to calculate it is like this.....
eks.. 1234*1234
on paper we put it up like this..
1234
1234
------
answer: 1522756
we start with multiplying 4*4 =6, 1 to reminder
then 3*4 + 4*3 + reminder=5, 2 to reminder
then 2*4 + 3*3 + 4*2 + reminder=7, 2 to reminder
then 1*4 + 2*3 + 3*2 + 4*1 + reminder=2, 2 to reminder
then 1*3 + 2*2 + 3*1 + reminder= 2, 1 to reminder
then 1*2 + 2*1 + 1 + reminder = 5
then 1* 1= 1
voila we have the answer 1522756..
You notice the cross multiplying here. This is an old multiplying method from India, our teacher sayed
our problem is to find the right design on our c++ code, how the algorithm and recursive loop are going to be. Our heads are bursting now, but we hope we can get some hints out there how to solve this "problem".

Lars and Jan..

 

[zBuilder]

Why not use strtod which converts a string to a double floating point and then use the normal C keywords to multiply the numbers? Or do you want to do it the hard way?


Kim_Christensen@telus.net

http://www3.bc.sympatico.ca/Kim_Christensen/index.html