计算机科学导论6.pptVIP

Chapter 6 Programming languages Outline Evolution Categories of languages Building programs Elements of programming languages Objectives Have a vision of computer language evolution. Distinguish between machine, assembly, and high-level languages. Distinguish between the different categories of languages: procedural, object-oriented, functional, declarative, and special. Understand the process of creating and running a program. Become familiar with elements of programming languages. part 1Evolution Evolution A computer language is a set of predefined words that are combined into a program according to predefined rules (syntax). Computer languages have evolved from machine language to natural languages. Machine languages Machine language, the lowest level of language, is the basic language of the computer, representing data as 1s and 0s. Machine programs vary from computer to computer; that is, they are machine dependent. The only language understood by a computer is machine language. These binary digits correspond to the on and off electrical states of the computer. Machine languages Advantage: it works efficiently for computer. Disadvantage: it is not convenient for people to read and use. Symbolic languages Symbolic language, also called assembly language, is a low-level language that allows a programmer to use abbreviations or easily remembered words instead of numbers. Assembly language varies from computer to computer; it’s machine dependent. A programmer can write instructions in assembly language more quickly than in machine language; however, it’s still not an easy one to learn, and it’s so tedious to use that mistakes are frequent. Symbolic languages Language translators A special program called an assembler is used to translate symbolic code into machine language. A language translator is a type of system software that translates a program written in a second- or higher-generation language into machine language. Language translators Languages trans