How to check if an integer can be divided by 3

Question

How to check if my integer can be divided by 3 as below:

for(int i=0; i<24;  i++){
   //here, how to check if "i" can be divided by 3 completely(e.g. 3, 6, 15)?

}

You have about 20 questions without an accepted answer. Perhaps you could ask clearer questions or follow up on answers so they can be accepted. — Peter Lawrey, Jul 11 '11 at 08:12
This question seems pretty clear to me. It's asking how to divide the current number in the loop by 3 and got no remainder. — Rich, Feb 16 '23 at 17:24

score 77 · Accepted Answer · answered Jul 11 '11 at 08:03

77

Use the modulo operator.

if(i % 3 == 0)

Also see Modulo operation at Wikipedia

answered Jul 11 '11 at 08:03

Sebastian Wramba

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score 10 · Answer 2 · answered Jul 11 '11 at 08:11

If you are using a loop, you can use the fact that every third number can be divided by 3.

for(int i = 0; i < 24;  i += 3) {
   System.out.println(i + " can be divided by 3");
   System.out.println((i+1) + " cannot be divided by 3");
   System.out.println((i+2) + " cannnot be divided by 3");
}

This avoids the need for a modulo and cuts the number of loops by a factor of 3.

score 6 · Answer 3 · answered Jul 11 '11 at 08:03

6

Use the MOD operator

for(int i=0; i<24;  i++){
   if( i%3 == 0 )
       // It is divisible by 3

}

answered Jul 11 '11 at 08:03

Talha Ahmed Khan

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score 5 · Answer 4 · edited May 23 '17 at 10:31

Well, what you could do (it might be a bit faster; it is faster on my machine) is:

boolean canBeDevidedBy3 = ((int) (i * 0x55555556L >> 30) & 3) == 0;

instead of

boolean canBeDevidedBy3 = (i % 3) == 0;

However, the multiplication trick only works for -2 <= i <= 1610612735. This answer was inspired by this optimization question. But if I can give you a tip: use (i % 3) == 0. It's so much simpler, and will always work.

score 4 · Answer 5 · answered Jul 11 '11 at 08:03

4

Check the remainder of i devided by 3

if (i % 3 == 0) {}

answered Jul 11 '11 at 08:03

Dimitar Petrov

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score 1 · Answer 6 · answered Jul 11 '11 at 08:04

1

inside the loop:

if (i%3 == 0)
    // it can be divided by 3

% is called "mod" or "modulus" and gives you the remainder when dividing two numbers.

These are all true:

6 % 3 == 0
7 % 3 == 1
7 % 4 == 3

answered Jul 11 '11 at 08:04

BudgieInWA

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score 0 · Answer 7 · answered Jul 11 '11 at 08:04

0

if( i % 3 == 0 )

The % operator delivers you the rest of the division i / 3

answered Jul 11 '11 at 08:04

Tim Meyer

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score 0 · Answer 8 · answered Jul 11 '11 at 08:04

0

if( i % 3 == 0 ){
System.out.println("can be divided by 3");
}else{
System.out.println("cant divide by 3");
}

Is this question for real?

answered Jul 11 '11 at 08:04

Benny Tjia

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How to check if an integer can be divided by 3

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