A do statement repeats a dependent statement or block while a condition remains true. Unlike while, it executes that body before testing the condition, so the first iteration is unconditional. section 3.0 section 3.2
while (condition) statement-or-block
do statement-or-block while(condition);
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The essential syntax places the condition after the body: do statement-or-block while (condition); The trailing semicolon is part of the do statement. section 3.2
Rewriting an iterative approximation
A Heron approximation can use a while loop when the condition is tested before each iteration. The do form moves the update first: do { x *= (2.0 - a*x); } while (fabs(1.0 - a*x) >= eps); Here, the approximation update runs once, then the product is tested to determine whether another iteration is needed. This expresses a process that must perform an update before checking whether it is close enough. section 3.2
TAKEAWAY
- Choose do when the body must run before its continuation condition is evaluated; choose while when the condition should be checked first. section 3.2
- Treat do as one of C’s three iteration statements alongside for and while; for remains the preferred form for domain iterations. section 3.4
