Chapter 3 Data types, Operators, and Expressions b3.2 Constants and variables Identifiers(标志符) An identifier is a sequence of letters, digits and underscore The first character must be a letter or an underscore Upper and lower case letters are different Can not use keywords as variable names It's wise to choose variable names that are related to the 例:判断下列标识符号合法性 sum Sum M.D.John day Date 3days student name #33 lotus 1 2 3 char a>b above $123 1010  3.2 Constants and Variables – Identifiers (标志符) • An identifier is a sequence of letters , digits and underscore _ ; • The first character must be a letter or an underscore _; • Upper and lower case letters are different ; • Can not use keywords as variable names ; • It’s wise to choose variable names that are related to the purpose of the variable ; Notice : such as l and I, o and 0…….. 例:判断下列标识符号合法性 sum Sum M.D.John day Date 3days student_name #33 lotus_1_2_3 char a>b _above $123 < > M.D.John 3days #33 char a>b $123 Chapter 3 Data types , Operators , and Expressions