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📝 [Flutter] learning to form a record, [programmer essential knowledge]

📔 The introduction and use of num, the basic data type of Flutter Dart.

1. Write at the front

The syntax and use of VAR, final, and const for Dart was introduced in the previous article, so let’s move on to the basic syntax for Dart.

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Dart uses var, final, and const

2. The value type is num

In dart, the numeric type number is divided into two types, int and double. Let’s look at the use of int first.

2.1 type int

void main(a){

  numTest();
}

void numTest(a){
  //number specifies the numeric type int and double
  num a = 1;
  print(a);
}
Copy the code

The running results are as follows:

2.2 type double

void numTest(a){
  //number specifies the numeric type int and double
  num a = 1;
  print(a);
  a = 3.4;
  print(a);
}
Copy the code

The running results are as follows:

Don’t have tonumDeclaration, can be used directlyint 和 doubleCan also.

void numTest(a){
  //number specifies the numeric type int and double
  num a = 1;
  print(a);
  a = 3.4;
  print(a);

  int b = 4;
  print(b);

  double c = 3.3;
  print(c);
}
Copy the code

Running results:

Double can be assigned to an int, but int cannot be assigned to a double.

2.3 Common Methods

There are some common methods, such as determining odd or even numbers, subtracting, multiplying, and dividing (+ – * /), modulo (%), and a special round (~/).

void numTest(a){
  //number specifies the numeric type int and double
  num a = 1;
  print(a);
  a = 3.4;
  print(a);

  int b = 4;
  print(b);

  double c = 3;// Equivalent to 3.0
  print(c);

  print(b.isEven);// Is it even
  print(b.isOdd);// Is it odd

  print(b~/c);/ / integer

}
Copy the code

The running results are as follows:

2.4 Type Conversion

Whether isEven isEven, whether isOdd isOdd, that’s only an int, so if you want to call a double, you need to cast it.

Ints can also be converted to double, and the types can be converted to each other.

3. Write in the back

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