The Hierarchy of Program Control Structures
Open Access
- 1 January 1986
- journal article
- Published by Oxford University Press (OUP) in The Computer Journal
- Vol. 29 (1) , 24-32
- https://doi.org/10.1093/comjnl/29.1.24
Abstract
The structural hierarchy of programs is presented in this paper. It is defined on the basis of a composition of control structures. It is shown that there is an infinite hierarchy ϕ1,ϕ2,… ϕn,… so that the control structures in ϕn cannot be expressed as a superposition of control structures in ∪k−1n−1ϕk unless we use new variables or GOTO statements. ϕ1 contains D-structures (Ref.7), ϕ2 contains cycles with two exits, ϕ3 is partly covered by Adams' (Ref.1) proposal. Three characterisations of ϕn are introduced and their hierarchy is inspected. From the hierarchy new control structures convenient for implementation are deduced. Our results show some limits of GOTO-less programming and indicate some reasons why GOTO statement has returned into programming languages.Keywords
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