C程序设计第七章函数.pptVIP

Chapter 7 - Functions 7.1 Introduction Divide and Conquer ——分而治之 Construct a program from smaller pieces or components Each piece more manageable than the original program 函数是一段完成特定任务的程序。 模块化程序设计 基本思想：将一个大的程序按功能分割成一些小模块 特点： 各模块相对独立、功能单一、结构清晰、接口简单 控制了程序设计的复杂性 提高元件的可靠性 缩短开发周期 避免程序开发的重复劳动 易于维护和功能扩充 开发方法: 自上向下，逐步分解，分而治之 7.2 Program Modules in C Functions Modules in C Programs written by combining user-defined functions with library functions C standard library has a wide variety of functions Makes programmers job easier - avoid reinventing the wheel 7.2 Program Modules in C (II) Function calls——函数调用 Invoking functions——调用函数 Provide function name and arguments (data) Function performs operations or manipulations Function returns results Boss asks worker to complete task Worker gets information, does task, returns result Information hiding: boss does not know details 7.3 Math Library Functions Math library functions perform common mathematical calculations #include math.h Format for calling functions FunctionName (argument); If multiple arguments, use comma-separated list printf( %.2f, sqrt( 900.0 ) ); Calls function sqrt, which returns the square root of its argument All math functions return data type double Arguments may be constants, variables, or expressions 7.4 Functions Functions Modularize a program All variables declared inside functions are local variables（局部变量） Known only in function defined Parameters Communicate information between functions Local variables Benefits Divide and conquer Manageable program development Software reusability Use existing functions as building blocks for new programs Abstraction - hide internal details (library functions) Avoids code repetition 7.5 Function Definitions Function definition format return-value-type function-name( parameter-list ){ declarations and statements} Function-name: any valid identifier Return-value-type: data type of the result (default int) void - function returns nothing Parameter-list: com