DoLoop

A DO LOOP is a control flow construct used in many imperative programming languages to repeat a block of statements. It can run a fixed number of times or continue until a specified condition is met.

Historically, explicit looping constructs emerged early in high-level languages. The Fortran DO loop is a classic fixed-count form, while other languages introduced similar looping mechanisms, such as BASIC's DO...LOOP and the various forms of for, while, and do-while loops found in modern languages. The general idea is to separate the repetitive task from its termination condition, allowing concise and readable code.

Common forms of a do loop appear across languages. In Fortran, a fixed-count loop takes the shape DO i = start, end, step; statements; END DO. In C-like languages, a for loop provides initialization, a test, and an update in a compact header, such as for (i = start; i <= end; i += step) { ... }. Do-while or Do-Until variants execute the body at least once and then test the condition. Some languages also offer Do ... Loop constructs with explicit While or Until conditions.

Typical uses include iterating over ranges or arrays, performing repeated calculations, or applying an operation to each element of a collection. Do loops are foundational for algorithms that require repeated processing, accumulation, or traversal.

Common pitfalls include off-by-one errors, infinite loops if the termination condition never becomes true, and modifying loop variables in ways that undermine the loop’s progress. Careful design of the loop’s bounds and increment is essential for correctness and performance.

See also: while loop, for loop, do-while loop, loop control statements.