CODEWITHSUNDEEP
c#
user1211185
user1211185

Reputation: 731

How to multiply decimal numbers without using multiplication(*) sign

Can anyone suggest me a way to multiply decimal numbers without using multiplication(*) sign. I know it looks like homework thing, but I just want to know how to achieve this. I have already done this for positive and negative integers as below: 

int first = 2;
int second =2;
int result = 0;
bool isNegative = false;

if (first < 0)
{
    first = Math.Abs(first);
    isNegative = true;
}
if (second < 0)
{
    second = Math.Abs(second);
    isNegative = true;
}

for (int i = 1; i <= second; i++)
{
    result += first;
}

if (isNegative)
    result = -Math.Abs(result);

Want to multiply this for decimals:

decimal third = 1.1;
decimal fourth = 1.2;

Thanks

Upvotes: 5

Views: 3888

Answers (5)

Matthew Strawbridge
Matthew Strawbridge

Reputation: 20610

Here's another approach, using rules of logs, for the sake of completeness:

decimal result = (decimal)Math.Exp(
    Math.Log((double)third) + Math.Log((double)fourth));

It's not going to work for all decimals (in particular not for negative numbers, although it could be extended to detect these and work around them), but it's interesting nevertheless.

Upvotes: 0

JacobD
JacobD

Reputation: 627

Strictly with out '*' ? I'd take note of the XOR operator implemented. Although I know this code is not much different to the OP's.

int first = 2;
int second =2;
int result = 0;
bool isNegative;

isNegative = (first<0)^(second<0);

first = (first<0)?Math.Abs(first):first;    
second = (second<0)?Math.Abs(second):second;

for (int i = 1; i <= second; i++)
    result += first;

result = (isNegative)?-Math.Abs(result):result;

Upvotes: 1

Scope Creep
Scope Creep

Reputation: 565

The simplest way to multiple two decimals without using the * operator is to use the Decimal.Multiply method.

Example:

decimal first = -2.234M;
decimal second = 3.14M;

decimal product = Decimal.Multiply(first, second);

Upvotes: 2

Jon Egerton
Jon Egerton

Reputation: 41539

Bit of a cheat, but if the task strictly relates to all forms of multiplication (rather than just the * operator), then divide by the reciprocal:

var result = first / (1 / (decimal)second);

Upvotes: 12

Tim Schmelter
Tim Schmelter

Reputation: 460078

Just another way ;)

if (second < 0)
{ 
    second = Math.Abs(second);
    first = (-1) * first;
}
result = Enumerable.Repeat(first, second).Sum();

Upvotes: 6

Related Questions