Do-While Loop

A do-while loop is a post-test iteration control structure in C that guarantees the execution of its statement block at least once. Unlike pre-test loops (such as while or for), the do-while loop evaluates its controlling expression at the bottom of the loop, strictly after the loop body has executed.

Syntax

do {
    // Loop body: statements to execute
} while (expression);

Execution Mechanics

1. Unconditional First Pass: Control flow enters the do block and executes the enclosed statements without any prior condition checks.
2. Expression Evaluation: After the loop body completes, the scalar expression within the while clause is evaluated.
3. Branching:
   • If the expression evaluates to a non-zero value (true), control flow jumps back to the top of the do block, initiating the next iteration.
   • If the expression evaluates to zero (false), the loop terminates, and control flow passes to the next sequential statement in the program.

Technical Characteristics

• Terminating Semicolon: The do-while construct strictly requires a semicolon ; immediately following the while (expression) clause. Omitting this is a common syntax error that will halt compilation.
• Scope: Variables declared inside the do block have block scope and are destroyed at the end of each iteration. They cannot be referenced in the while expression, as the expression sits outside the lexical scope of the loop body.
• Control Flow Interruption:
  • A break statement inside the body immediately terminates the loop, bypassing the while evaluation.
  • A continue statement inside the body skips the remaining statements in the current iteration and jumps directly to the while (expression) evaluation to determine if the loop should proceed.

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