whx第六课 变量、数据类型 与赋值运算 - 北京大学.ppt

Lesson 7 Processing and Interactive Input Hu Junfeng 2006/10/13 About homework :(2.6-4) About homework :(continue) About homework :(continue) About homework :(continue) Assignment (continue) Increment operator (++): variable = variable + 1 can be replaced by variable++ or ++variable #include stdio.h main() { int x=23; printf(%d\n,--x); } Mathematical Library Functions #include math.h A First Look at User-Input Validation (continued) As written, Program 3.12 is not robust The problem becomes evident when a user enters a non-integer value Enter three integer numbers: 10 20.68 20 The average of 10, 20, and -858993460 is -286331143.333333 Handling invalid data input is called user-input validation Validating the entered data either during or immediately after the data have been entered Providing the user with a way of reentering any invalid data Formatted Output (continued) Other Number Bases Other Number Bases (continued) The decimal value of the letter a is 97. The octal value of the letter a is 141. The hex value of the letter a is 61. Symbolic Constants (continued) Symbolic Constants Literal data refers to any data within a program that explicitly identifies itself Literal values that appear many times in the same program are called magic numbers C allows you to define the value once by equating the number to a symbolic name #define SALESTAX 0.05 #define PI 3.1416 Also called symbolic constants and named constants Summary Arithmetic calculations can be performed using assignment statements or mathematical functions The assignment symbol, =, is an operator C provides the +=, -=, *= and /= assignment operators The increment operator, ++, adds 1 to a variable The decrement operator, --, subtracts 1 from a variable C provides library functions for calculating square root, logarithmic, and other mathematical computations Summary (continued) Mathematical functions may be included within larger expressions scanf() is a standard library fu