Type Conversion in Dart

What is Type Conversion?

Type conversion (or type casting) is the process of changing a value from one data type to another. In Dart this is always explicit — you must intentionally convert a value; Dart will not silently convert types for you.

String to Number

// String → int
String s1 = '42';
int n1 = int.parse(s1);
print(n1 + 8);   // 50

// String → double
String s2 = '3.14';
double n2 = double.parse(s2);
print(n2 * 2);   // 6.28

// Safe parsing (no exception on failure)
int? safe = int.tryParse('abc');
print(safe);     // null

Number to String

int n = 100;
double d = 3.14159;

String s1 = n.toString();           // '100'
String s2 = d.toString();           // '3.14159'
String s3 = d.toStringAsFixed(2);   // '3.14'
String s4 = n.toRadixString(16);    // '64' (hex)

print(s1 + ' dollars');             // 100 dollars

int to double

int i = 5;
double d = i.toDouble();   // 5.0
double d2 = i / 1;         // also 5.0 (division always returns double)
print(d);  // 5.0

double to int

double d = 9.99;
int i1 = d.toInt();       // 9  (truncates decimal)
int i2 = d.round();       // 10 (rounds to nearest)
int i3 = d.ceil();        // 10 (rounds up)
int i4 = d.floor();       // 9  (rounds down)
print('$i1 $i2 $i3 $i4'); // 9 10 10 9

Boolean Conversions

Dart does not automatically convert other types to bool. Use explicit comparisons:

int n = 0;
// bool b = n;  ← ERROR in Dart
bool b = n != 0;    // explicit conversion: false
bool b2 = n == 0;   // true

String s = '';
bool isEmpty = s.isEmpty;  // true

Full Example

void main() {
  // Simulating user input as strings
  String ageInput = '25';
  String heightInput = '5.9';

  int age = int.parse(ageInput);
  double height = double.parse(heightInput);

  print('Age: $age ($${age.runtimeType})');
  print('Height: $height ($${height.runtimeType})');

  // Convert back to string for display
  String summary = 'Age $age, Height $${height.toStringAsFixed(1)} ft';
  print(summary);

  // int ↔ double
  double ageDouble = age.toDouble();
  int heightInt = height.toInt();
  print('Age as double: $ageDouble');
  print('Height as int: $heightInt');
}

Age: 25 (int)
Height: 5.9 (double)
Age 25, Height 5.9 ft
Age as double: 25.0
Height as int: 5

🧠 Quiz

Summary

Dart type conversion is always explicit. Convert strings to numbers with int.parse() / double.parse(). Convert numbers to strings with toString() / toStringAsFixed(). Convert between int and double with toDouble() / toInt(). Use tryParse() for safe parsing that returns null on failure.