CHAPTER 2 - PSEUDOCODE AND NASSI–SCHNEIDERMAN DIAGRAMS

Abstract

This chapter discusses pseudocode and Nassi-Schneiderman diagrams. It presents six basic computer operations and introduces common words and keywords which are used to represent the operations in pseudocode. Each operation can be represented as a straightforward English instruction, with keywords and indentation to signify a particular control structure. The Structure Theorem forms the basic framework for structured programming. It states that it is possible to write any computer program by using only three basic control structures, viz. sequence, selection and repetition. These control structures are easily represented in pseudocode and Nassi-Schneiderman diagrams. The sequence control structure is defined as the straightforward execution of one processing step after another. A Nassi-Schneiderman diagram represents this control structure as a series of rectangular boxes. The sequence control structure can be used to represent the first four basic computer operations. The selection control structure can be defined as the presentation of a condition, and the choice between two actions depending on whether the condition is true or false. This construct represents the decision making abilities of the computer and is used to illustrate the fifth basic computer operation. The repetition control structure can be defined as the presentation of a set of instructions to be performed repeatedly, as long as a condition is true.