Dart Do-While Loop

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Syntax

do {
  // Statement(s) to execute
} while (condition);

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Execution Flow

1. Execution: The statement(s) inside the do block are executed immediately.
2. Evaluation: The condition expression is evaluated.
3. Branching:
   • If the condition evaluates to true, control flow returns to the beginning of the do block.
   • If the condition evaluates to false, the loop terminates, and control flow proceeds to the next statement in the program.

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Code Example

int counter = 0;

do {
  print('Iteration: $counter');
  counter++;
} while (counter < 3);

Iteration: 0
Iteration: 1
Iteration: 2

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Technical Characteristics

• Strict Boolean Evaluation: Dart enforces strict type safety. The condition expression must evaluate to a literal bool type. Dart does not support “truthy” or “falsy” type coercion (e.g., while (1) will result in a compile-time error).
• State Mutation: To prevent infinite loops, the block of code within the do statement must eventually mutate the state evaluated in the while condition, or utilize a control transfer statement like break.
• Scope: Variables declared inside the do block are block-scoped and cannot be accessed within the while condition. Variables evaluated in the condition must be declared in an outer scope prior to the loop.

// Invalid Scope Example
do {
  int x = 5; 
} while (x > 0); // Error: 'x' is undefined in this scope.

// Valid Scope Example
int y = 5;
do {
  y--;
} while (y > 0); // Valid: 'y' is declared in the outer scope and mutates to terminate.