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Short-circuit evaluation, instead of full evaluation, of Boolean expressions is a technique used in programming languages to save execution time and prevent run-time errors. In addition, use of short-circuiting may save space for the object code needed to evaluate Boolean expressions. In this article we show that whether shortcircuit or full evaluation requires less space depends on the processor architecture, the type of expression, and the compiler. After examining the types of Boolean expressions commonly used in programs, we give the minimal instruction sequences needed for their evaluation on a CISC architecture, a stack architecture, and a RISC architecture. We show that for commonly used architectures and Boolean expressions, short-circuit evaluation often requires less space for object code than full evaluation.

This is the 23rd Self-Assessment Procedure. 1 The purpose of this procedure is to let its readers test their knowledge of some of the more important features of significant programming languages. The features of imperative languages like Fortran, Algol 60, PL/I, Pascal, Modula-2, C, and Ada considered are data types, data structures, control structures, program units, scope of names, and parameter passing. Some of the corresponding features of functional languages like Lisp, logic programming languages like Prolog, and ohject-oriented programming languages like C++ and Smalltalk, are reviewed. Finally brief consideration is given to syntax and semantics, chiefly by reference to the Backus-Naur form, BNF. The features of programming languages affect all aspects of programming, including the ease of writing and maintaining programs, the reliahility of software, and the efficiency and portability of programs. Knowledge of programming language concepts and constructs is of importance to software developers, programmers, and designers of programming languages and compilers. The topic of this procedure should be of interest to any computer science student or practitioner who wishes to test his or her knowledge and learn more about one of the most important and broad areas in the computer field. The language used most often in the questions is Pascal, with Ada, Lisp, and Prolog also featured prominently. A glossary is included which defines some of the terms used in the procedure. The questions are either multiple-choice or short answer. Some of the multiple-choice questions allow for more than one correct answer.