> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/NormandoRamirezDelgado/6C-Febrero-2026/llms.txt
> Use this file to discover all available pages before exploring further.
# Type Conversions
> Learn how to convert between different data types in Dart
## Introduction
Type conversion (also called type casting) is the process of converting a value from one data type to another. In Dart, you'll often need to convert between types, such as turning a String into an int, or an int into a double.
Dart performs **explicit type conversion** - you must explicitly convert types using built-in methods. This prevents accidental type-related bugs.
## Common Type Conversions
Parse text to integer
Convert number to text
Convert integer to decimal
Convert decimal to integer
Parse text to decimal
Convert decimal to text
## String to int Conversion
Use `int.parse()` to convert a String containing a number into an integer:
```dart theme={null}
void main() {
String variable = '50';
// Convert String to int
int numero = int.parse(variable);
print(numero); // 50 (as integer)
print(numero + 10); // 60 (can now do math)
}
```
`int.parse()` will throw an error if the string doesn't contain a valid integer. For example, `int.parse('hello')` will crash your program.
### Safe Parsing with tryParse
For safer parsing that won't crash your program, use `int.tryParse()`:
```dart theme={null}
void main() {
String validNumber = '42';
String invalidNumber = 'hello';
int? result1 = int.tryParse(validNumber); // 42
int? result2 = int.tryParse(invalidNumber); // null
print(result1); // 42
print(result2); // null
}
```
## int to String Conversion
Use `.toString()` to convert any number to a String:
```dart theme={null}
void main() {
int numero = 50;
// Convert int to String
String valor = numero.toString();
print(valor); // '50' (as String)
print(valor + ' km'); // '50 km' (string concatenation)
}
```
### Working with Large Numbers
```dart theme={null}
void main() {
int numeroUno = 123;
int numeroDos = 6524200889711234;
print(numeroDos); // 6524200889711234
print(numeroDos.toString()); // '6524200889711234'
}
```
## int to double Conversion
Use `.toDouble()` to convert an integer to a double (decimal number):
```dart theme={null}
void main() {
int numeroUno = 123;
// Convert int to double
double dobleUno = numeroUno.toDouble();
print(numeroUno); // 123
print(dobleUno); // 123.0
}
```
Converting to double is useful when you need decimal precision in calculations, even if your starting value is a whole number.
## double to int Conversion
Use `.toInt()` to convert a double to an integer. **This truncates the decimal part** (doesn't round):
```dart theme={null}
void main() {
double dobleDos = 1234523456243563567.86348623487623465;
// Convert double to int (truncates decimal)
int entero = dobleDos.toInt();
print(dobleDos); // 1.2345234562435636e+18
print(entero); // 1234523456243563520
}
```
`.toInt()` **truncates** (cuts off) the decimal part, it doesn't round. For example:
* `3.9.toInt()` returns `3` (not `4`)
* `3.1.toInt()` returns `3`
* `-3.9.toInt()` returns `-3`
### Rounding Doubles to Integers
If you want to round instead of truncate, use these methods:
```dart theme={null}
void main() {
double number = 3.7;
print(number.toInt()); // 3 (truncate)
print(number.round()); // 4 (round to nearest)
print(number.floor()); // 3 (round down)
print(number.ceil()); // 4 (round up)
}
```
## String to double Conversion
Use `double.parse()` to convert a String to a double:
```dart theme={null}
void main() {
String precio = '19.99';
// Convert String to double
double valor = double.parse(precio);
print(valor); // 19.99
print(valor * 2); // 39.98
}
```
## Complete Conversion Example
Here's a comprehensive example showing all the common conversions:
```dart theme={null}
void main() {
// String to int
String variable = '50';
int numero = int.parse(variable);
print('String to int: $numero');
// int to String
String valor = numero.toString();
print('int to String: $valor');
// int to double
int numeroUno = 123;
double dobleUno = numeroUno.toDouble();
print('int to double: $dobleUno');
// double to int
double dobleDos = 1234.56789;
int entero = dobleDos.toInt();
print('double to int: $entero');
// String to double
String textoDecimal = '99.99';
double precio = double.parse(textoDecimal);
print('String to double: $precio');
// double to String
String precioTexto = precio.toString();
print('double to String: $precioTexto');
}
```
## Practical Use Cases
### User Input Conversion
```dart theme={null}
void main() {
// User inputs are always strings
String userInput = '25'; // Simulating user input
// Convert to int for calculations
int edad = int.parse(userInput);
if (edad >= 18) {
print('You are an adult');
} else {
print('You are a minor');
}
}
```
### Calculations with Mixed Types
```dart theme={null}
void main() {
int quantity = 5;
double pricePerUnit = 12.50;
// Convert int to double for precise calculation
double total = quantity.toDouble() * pricePerUnit;
print('Total: \$${total}'); // Total: $62.5
}
```
### Formatting Numbers for Display
```dart theme={null}
void main() {
int score = 95;
double average = 87.5;
// Convert to strings for display
String message = 'Score: ${score.toString()}, Average: ${average.toString()}';
print(message);
}
```
## Conversion Methods Summary
| From | To | Method | Example |
| ------ | ----------- | ---------------- | ------------------------------- |
| String | int | `int.parse()` | `int.parse('42')` → `42` |
| String | int (safe) | `int.tryParse()` | `int.tryParse('42')` → `42` |
| String | double | `double.parse()` | `double.parse('3.14')` → `3.14` |
| int | String | `.toString()` | `42.toString()` → `'42'` |
| int | double | `.toDouble()` | `42.toDouble()` → `42.0` |
| double | String | `.toString()` | `3.14.toString()` → `'3.14'` |
| double | int | `.toInt()` | `3.14.toInt()` → `3` |
| double | int (round) | `.round()` | `3.14.round()` → `3` |
| double | int (floor) | `.floor()` | `3.9.floor()` → `3` |
| double | int (ceil) | `.ceil()` | `3.1.ceil()` → `4` |
## Error Handling
Always validate string input before parsing to avoid runtime errors:
```dart theme={null}
void main() {
String input = 'not a number';
// ❌ BAD: Will crash if input is invalid
// int number = int.parse(input); // FormatException!
// ✅ GOOD: Safe parsing
int? number = int.tryParse(input);
if (number != null) {
print('Valid number: $number');
} else {
print('Invalid input');
}
}
```
## Key Takeaways
* Use `int.parse()` or `int.tryParse()` to convert String to int
* Use `double.parse()` or `double.tryParse()` to convert String to double
* Use `.toString()` to convert any number to String
* Use `.toDouble()` to convert int to double
* Use `.toInt()` to convert double to int (truncates decimals)
* Use `.round()`, `.floor()`, or `.ceil()` for rounding doubles
* Always handle potential parsing errors with `tryParse()` methods
## Next Steps
Now that you understand type conversions, you're ready to explore operators and how to perform calculations and comparisons in Dart.