The 'while' Loop

Part of the Fundamentals section of Coddy's Dart journey — lesson 43 of 94.

The while loop in Dart repeatedly executes code while a condition is true, ideal when iteration count is unknown.

void main() {
  int count = 1;
  
  while (count <= 5) {
    print(count);
    count++;
  }
}

Output:

Basic structure:

while (condition) {
  // Code to repeat
}

Calculating a sum:

void main() {
  int sum = 0;
  int i = 1;
  
  while (i <= 5) {
    sum += i;
    i++;
  }
  
  print("Sum: $sum");
}

Output:

Sum: 15

Challenge

Beginner

In this challenge, you'll practice using the while loop in Dart to count down from a given number to 1.

Your task is to create a program that:

Reads a single integer n from the input
Uses a while loop to print a countdown from n to 1, each on a new line
After the countdown, prints Blastoff!
Finally, prints the sum of all numbers in the countdown

For example, if the input is 5, your program should output:

5
4
3
2
1
Blastoff!
Sum: 15

Notice that each number is printed on a new line, followed by "Blastoff!" on its own line, and then the sum is printed with the format Sum: X where X is the calculated sum.

Cheat sheet

The while loop repeatedly executes code while a condition is true:

while (condition) {
  // Code to repeat
}

Basic counting example:

int count = 1;

while (count <= 5) {
  print(count);
  count++;
}

Calculating a sum with while loop:

int sum = 0;
int i = 1;

while (i <= 5) {
  sum += i;
  i++;
}

print("Sum: $sum");

Try it yourself

import 'dart:io';

void main() {
  // Read input
  String? input = stdin.readLineSync();
  
  // Convert input to integer
  var n = int.tryParse(input ?? '0') ?? 0;
  
  // TODO: Implement a while loop to count down from n to 1
  // and calculate the sum of all numbers
  
  // TODO: Print "Blastoff!" after the countdown
  
  // TODO: Print the sum with the format "Sum: X"
}