unit-8数据结构与算法.pptVIP

You may also need to know how to iterate through all the items in a data structure, visiting each one in turn so as to display it or perform some other action on it. One important algorithm category (7) is sorting. There are many ways to sort data，The concept of recursion is important in designing certain algorithms (1)Problems with Procedural(9) Languages OOP was invented because procedural languages, such as C, Pascal, and BASIC, were found to be inadequate (10) for large and complex programs. Why was this? The problems have to do with the overall organization of the program. Procedural programs are organized by dividing the code into functions (called procedures or subroutines in some languages).注7 Groups of functions could form larger units called modules or files. Crude Organizational Units One difficulty with this kind of function-based organization was that it focused on functions at the expense of data. There werent many options when it came to data. To simplify slightly, data could be local to a particular function or it could be global—accessible (11) to all functions. There was no way (at least not a flexible way) to specify that some functions could access a variable (12) and others couldnt. This caused problems when several functions needed to access the same data. To be available to more than one function, such variables had to be global, but global data could be accessed inadvertently (13) by any function in the program.注8 This leads to frequent programming errors. What was needed was a way to fine-tune data accessibility, allow in variables to be available to functions with a need to access it, but hiding it from others. From The idea of objects arose in the programming community as a solution to the problems with procedural languages. This new entity (14), the object, solves several problems simultaneously (15). Not only does a programming object correspond more accurately (16) to objects in the real world, it also solves the problem engender