1将字符串给整形变量 2字符数据与整数进行算术运算，将小写转大写 3符号常量使用 4强制类型转换 5将有符号数据传送给无符号变量-1 to 2 string variables to the plastic character data and integer arithmetic operations to be lower case to upper case 3, the constant use of symbols 4 mandatory conversion 5 da