[Exercise] Decimal multiplication

Joe

Given two decimal numbers as strings of arbitrary length, multiply them.

eurybaric

import javax.swing.JOptionPane;

public static Multiply{

	public static void main{
	
	double num1;
	double num2;
	
	num1=Double.parseDouble(JOptionPane.showInputDialog("Enter first decimal");
	num2=Double.parseDouble(JOptionPane.showInputDialog("Enter second decimal");
	JOptionPane.showMessageDialog(null, "num1 * num2 = " + num1*num2);
	}
	}

Lamest? :)) havent tested but wtf it should work

Ayman

@eurybaric the aim of the exercise(most probably) is to actually implement an algorithm that converts the string into a decimal. i.e. something similar to what goes under the hood inside the parseDouble() function.

Or else would be too trivial to post as an exercise.

Joe

@eurybaric: Obviously, you cannot rely on the fact that your language already has float (or double) arithmetic. Use only int/long and strings.

Here's my code so far:

import sys

def f(s):
    a = s.find('.')
    return (int(s[:a]+s[a+1:]), len(s)-(a+1))
    

tot=1
dec=0

for i in map(f, sys.argv[1:]):
    tot *= i[0]
    dec += i[1]

stot = str(tot)
slen = len(stot) - dec

print stot[:slen] + "." + stot[slen:]

It (kinda) works:

$ ./dec_mult.py 3.1 12.1
37.51

It's very rudimentary, and will probably break on any input slightly more complex than the given example. (It breaks if the input string doesn't have a dot in it...).

I'll be updating this soon after work.