Way to combine integer array to a single integer variable? [duplicate]

Question

After finding the individual digits of a number by remainder procedure, the numbers are saved in an array. What I want now is to take the individual elements of this array and make a single integer value of it.

eg.

int a = 4400

digits saved in array by using recursion (4400/10) : let array be arr[]

arr[0]=0;
arr[1]=0;
arr[2]=4;
arr[3]=4;

final value:

int b= 4400 (by combining elements of array)

So I want to know if there is any way to combine the array elements to a single integer value ?

There is a way. It is similar to the way you decomposed it. Please make a try. — dotvav
– dotvav, Commented Nov 9, 2015 at 11:05

Andy Turner · Accepted Answer · 2015-11-09 11:21:38Z

3

Just multiply and add the digits:

int result = 1000 * arr[3] + 100 * arr[2] + 10 * arr[1] + arr[0];

Or, if you need it to work for any length of array (up to the number of digits in Integer.MAX_VALUE):

int result = 0;
for (int i = arr.length - 1; i >= 0; --i) {
  result = 10*result + arr[i];
}

edited Nov 9, 2015 at 11:21

answered Nov 9, 2015 at 11:15

Andy Turner

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1 Comment

The Law Over a year ago

Using i-- should be avoided in loops when possible, because it goes even further against what you could consider human mathematical and logical reasoning. Just leaving this comment here for new users searching same answer.

JBiss · Accepted Answer · 2015-11-09 11:16:02Z

2

I would use a stringbuilder.

StringBuilder builder = new StringBuilder();
builder.append(arr[3]);
builder.append(arr[2]);
builder.append(arr[1]);
builder.append(arr[0]);
System.out.println("Combined value is: " + Integer.parseInt(builder.toString());

edited Nov 9, 2015 at 11:16

answered Nov 9, 2015 at 11:10

JBiss

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3 Comments

Flown Over a year ago

As you can see in the question final value should be an int again.

Andy Turner Over a year ago

The result is not an int, and the digits are reversed.

JBiss Over a year ago

I have edited the answer

The Law · Accepted Answer · 2015-11-09 11:18:01Z

0

How about using simple loop and multiplication (assuming you know basic math)

int b = 0;
int z = 10;
for (int i = 1; i <= arr.length; i++) {
   b = (int) (b + (arr[i - 1] * Math.pow((double) z, i - 1)));
}

answered Nov 9, 2015 at 11:18

The Law

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