Any programming language in which sections of source code contained within pairs of matching delimiters such as "{" and "}" (e.g. in C) or "begin" and "end" (e.g. Algol) are executed as a single unit. A block of code may be the body of a subroutine or function, or it may be controlled by conditional execution (if statement) or repeated execution (while statement, for statement, etc.). In all but the most primitive block structured languages a variable's scope can be limited to the block in which it is declared. Block-structured languages support structured programming where each block can be written without detailed knowledge of the inner workings of other blocks, thus allowing a top-down design approach. See also abstract data type, module.