Do-while

The do-while and while loops are two types of loops in Dart used to repeat a block of code. However, there is a crucial difference between them: The while loop checks the condition before executing the code block, while the do-while loop checks the condition after completing the code block.

It means that the while loop may not execute at all if the condition does not evaluate to true on the first check. On the other hand, the do-while loop will consistently execute at least once, even if the condition does not evaluate to true on the first check.

Syntax

We write commands that should work in a loop in the do block of code;
This is the condition that determines whether to continue iterating the loop.

Example

Let's create a loop with a condition that will never be true:

main


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void main() {
  // `do-while` loop
  var counter = 5; // Declare and initialize the variable with `var`

  do {
    print('Do-while loop');   
    counter = counter + 1;
  } while (counter == 5); // Change the condition to 5
}

As you can see, the do-while loop executed the code block at least once, even if the condition counter != 0 was not evaluated to true on the first check.

Here is another way to understand the difference between the do-while and while loops:

The while loop is like checking before eating. You can only eat once you check if you are hungry;
The do-while loop is like eating before checking. You can eat, even if you are not hungry, and then check if you are still hungry.

Which type of loop to choose depends on your specific needs. Use a do-while loop if you want the code block to execute at least once. If you do not wish for the code block to run if the condition does not evaluate to true on the first check, use a while loop.

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Introduction to Dart

Do-while

Syntax

Example

What does the syntax of a do-while loop look like?