How to convert a double to an int in Dart?

Question

The following produces the below error:

int calc_ranks(ranks)
{
  double multiplier = .5;
  return multiplier * ranks;
}

The return type double is not a int, as defined by the method calc_ranks. How do I round/cast to an int?

Solution 1

Round it using the round() method:

int calc_ranks(ranks) {
    double multiplier = .5;
    return (multiplier * ranks).round();
}

Solution 2

You can use any of the following.

double d = 20.5;
int i = d.toInt(); // i = 20
int i = d.round(); // i = 21
int i = d.ceil();  // i = 21
int i = d.floor(); // i = 20

Solution 3

You can simply use toInt() to convert a num to an int.

int calc_ranks(ranks)
{
  double multiplier = .5;
  return (multiplier * ranks).toInt();
}

Note that to do exactly the same thing you can use the Truncating division operator :

int calc_ranks(ranks) => ranks ~/ 2;

Solution 4

I see a lot of answers, but with less description. Hope my answer will add some value. Lets initalize the variable, and see how it will change with different methods.

 double x = 8.5;

toInt()

It truncates the decimal value.

 int a = x.toInt();
 print(a); // 8

---

truncate()

It also truncates the decimal value.

 int b = x.truncate();
 print(b); // 8

---

round()

It returns the closest integer. It uses half up rounding mode.

  int c = x.round();
  print(c); // 9

---

ceil()

It returns the closest integer greater than the value.

  int c = x.ceil();
  print(c); // 9

---

floor()

It returns the closest integer smaller than the value.

  int c = x.floor();
  print(c); // 8

---

Solution 5

Dart round double to int

Using round() method, we can get an integer closest to a double.

For example:

int num1 = (2.3).round();
// 2
int num2 = (2.5).round();
// 3
int num3 = (-2.3).round();
// -2
int num4 = (-2.5).round();
// -3

You can also try to those methods convert double to int in a Flutter

  double x = 2.5;
  int a = x.toInt();
  int b = x.truncate();
  int c = x.round();
  int d = x.ceil();
  int e = x.floor();
  print(a); // 2
  print(b); // 2
  print(c); // 3
  print(d); // 3
  print(e); // 2

View more solutions

Comments

[Everton]

Or truncate it to int: return (multiplier * ranks).toInt(); (see api.dartlang.org/docs/channels/stable/latest/dart_core/…)

[最白目]

@Evertion I had cases where (0.57 * 100).toInt() resolved to 56, so guys, be careful.

[Hector Aguero]

So, what is the difference between toInt and floor or round and ceil

[iDecode]

First, this question wasn't about what round means in Dart. Second, the rest of the things are only copied from the existing answer. Please don't spam SO like this. You're only COPYING other answers.

[Ruben]

@iDecode Q: "How to convert a double to an int in Dart?" This Answer: "Using round() we can get an integer closest to a double". How come you think the answer is not related to the question?

[iDecode]

@Ruben This answer is already provided by other user. There's no benefit in posting same thing over and over again.

[Paresh Mangukiya]

I have already told you that from now on I will take care, even then why are you leaving a comment by down-voting. While the method is the same in this, but try to explain it differently, in this way I have given an example of how to take the number

[Paresh Mangukiya]

In this I have tried to explain how an integer is closest to a double. by this int num1 = (2.3).round(); // 2 int num2 = (2.5).round(); // 3 int num3 = (-2.3).round(); // -2 int num4 = (-2.5).round(); // -3

[Kamil Poniewierski]

Floor and ceil would convert the double to closest int, going down and up respectively, so (20.1).floor() would be 20, (20.1).ceil() would be 21. toInt cuts off the mantissa, leaving just the characteristic, and round makes it so the numbers with mantissa below 0.5 go down, others go up.