Building a Temperature Converter in Dart

Hello and welcome to the first of our #Dart30 series, where we’ll be creating 30 projects in 30 days using Dart programming language. Today, we’ll be building a simple yet practical project - a temperature converter that can convert temperatures from Celsius to Fahrenheit and vice versa.

Introduction to the Project

Our temperature converter is a command-line application. The user will input a temperature value, and then select whether they want to convert it to Fahrenheit or Celsius. The program will then perform the appropriate conversion and output the result.

The Code

Before we dive in, here’s the complete code for the project:

import 'dart:io';

void main() {
  stdout.write('Enter temperature: ');
  var input = stdin.readLineSync();

  stdout.write('Convert to (F)ahrenheit or (C)elsius? ');
  var choice = stdin.readLineSync()?.toLowerCase();

  var temperature = double.tryParse(input ?? '');
  if (temperature == null) {
    print('Invalid temperature input');
    return;
  }

  double result;
  String unit;

  if (choice == 'f') {
    result = temperature * 9 / 5 + 32;
    unit = 'F';
  } else if (choice == 'c') {
    result = (temperature - 32) * 5 / 9;
    unit = 'C';
  } else {
    print('Invalid choice');
    return;
  }

  print('$temperature° ${unit == 'F' ? 'C' : 'F'} is $result° $unit');
}

Now let’s break this down.

The main() Function

In Dart, the main function is the starting point of any application. It’s like the conductor in an orchestra, signaling when and how the different parts should start.

void main() {
  // rest of the code
}

User Input

The next section deals with taking input from the user. We use stdout.write to prompt the user for their input, and stdin.readLineSync() to capture it. The stdout and stdin comes from the dart:io library so make sure to import it at the top of your file.

// import
import 'dart:io';

// rest of the code inside main()
stdout.write('Enter temperature: ');
var input = stdin.readLineSync();

stdout.write('Convert to (F)ahrenheit or (C)elsius? ');
var choice = stdin.readLineSync()?.toLowerCase();

Here, stdout.write is like a television announcer asking a question, and stdin.readLineSync() is like our program tuning in to the microphone to hear the user’s answer.

Parsing the Input

After collecting the input, we need to make sure it’s in the format we can work with. We use double.tryParse to convert the input string to a double (a decimal number).

var temperature = double.tryParse(input ?? '');
if (temperature == null) {
  print('Invalid temperature input');
  return;
}

This is like a translator, taking a phrase in a foreign language (the string input) and converting it into our native language (a double).

Performing the Conversion

Now comes the soul of our project: converting the temperature based on the user’s choice.

double result;
String unit;

if (choice == 'f') {
  result = temperature * 9 / 5 + 32;
  unit = 'F';
} else if (choice == 'c') {
  result = (temperature - 32) * 5 / 9;
  unit = 'C';
} else {
  print('Invalid choice');
 return;
}

Think of this part like a traffic cop at a junction. Depending on the direction (choice) the driver (user) wants to go, the cop guides them onto the correct road (conversion formula).

Displaying the Result

Finally, we display the result of the conversion to the user.

print('$temperature° ${unit == 'F' ? 'C' : 'F'} is $result° $unit');

This is like the finale of a magic trick, where the magician reveals the transformed item to the audience.

Conclusion

That wraps up our first project in the #Dart30 series! Our temperature converter might be simple, but it showcases some fundamental Dart concepts like input/output, variable types, conditionals, and arithmetic operations. Keep practicing, and stay tuned for our next project!

Happy coding!

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