CODEWITHSUNDEEP
javaarraysdebugging
coinbird
coinbird

Reputation: 1217

Division not working with an array length JAVA

I'm trying to divide two numbers to get a percentage, then print it. Here's the relevant method:

public void process_winner(String candidates[], int votes[])
{
   double percent = (mostVotes / votes.length) * 100;
   if (mostVotes > votes.length / 2)
      System.out.println("Winner: " + candidates[mostVotesIndex] + "(" + percent + "%)");
   else
      System.out.println("None (no majority)");
   System.out.println("");
}

the problem line is:

double percent = mostVotes / votes.length;

mostVotes is an int, with a value of 6, and votes.length is 10. I verified this using the debugger.

It's showing a value of 0.0 for my percent variable, when it should show 60.0

Upvotes: 1

Views: 2198

Answers (5)

CatCoder
CatCoder

Reputation: 1

You need to change this or "cast" it to a double. what you have done is this

 double percent = (mostVotes / votes.length) * 100;

what you think you are doing is this:

  • (6/10) = 0.6
  • 0.6*100 = 60

now what is actually happening is this:

  • (6/10) = 0 <--- this is becasue it is an "Integer" division meaning it is not capable of dividing and creating a double data value. What it will do is change it to zero because an integer cannot produce a decimal digit
  • Therefore , 0*100 = gives you a 0 at the end

Know after explaining what you have done wrong i will explain what is right, and explain it to you.

  • you first "multiply" mostvotes with 100: (mostVotes*100) now this will create a full number; an integer.
  • now 6*100 = 600.
  • we then divide that with votes.length, which is "10"

  • we then recieve 60. <--- which is your answer.

    (mostVotes*100) / votes.length

The reason behind this is because you never really meet a decimal number in this way of calculation.

  1. you first 6*100 = 600 <--- no decimal (no double involved)
  2. Then you do 600/10 = 60 <--- no decimal (no double involved)

You of course can just change mostVotes into a double. But doing this is just a more convienent way.

This is more of a "algorithmic problem" and not a progrtamming problem.

Upvotes: 0

Rahul
Rahul

Reputation: 45070

You need to cast it to double, because otherwise it will be an integer division, and thus, the precision will be lost.

double percent = ((double) mostVotes / votes.length) * 100;

Upvotes: 3

Prasad Kharkar
Prasad Kharkar

Reputation: 13566

make your formule as (mostvotes * 100)/votes.length
In your case, the execution is:

  • mostVotes/votes.length causes 6/10 which is integer division
  • 6/10 = 0
  • 0 * 100 gives result 0

When you change it to double percent = (mostVotes * 100 ) / votes.length;

The order of execution becomes

  • mostVotes * 100 i.e. 6 * 100
  • 6 * 100 = 600.
  • 600/votes.length i.e. 600/10 = 60

This should give you correct output

Upvotes: 1

BobTheBuilder
BobTheBuilder

Reputation: 19294

This is Integer division, and works as expected.
If you want to get double value when dividing integers, use:

double percent = mostVotes * 1.0 / votes.length;

BTW, in order to get percentage, you need to multiple it by 100:

double percent = mostVotes * 100.0 / votes.length;

Upvotes: 1

RamonBoza
RamonBoza

Reputation: 9038

You need to cast to double, or change the operation order.

Do this:

double percent = (mostVotes * 100 ) / votes.length;

Upvotes: 5

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