2、定义一个学生类Student,它继承自person类。

不知道要那个toString()方法有什么用，回去好好看看方法的重写和重载去，总是看你提问题了，怎么老不会做呢！郁闷！下次自己写！ //父类 public class person { String name; String sex; int age; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String toString(){ return null; } public person(String name, String sex, int age) { this.name = name; this.sex = sex; this.age = age; } } //子类 public class Student extends person { long number; int phi; int eng; int comp; public long getNumber() { return number; } public void setNumber(long number) { this.number = number; } public int getPhi() { return phi; } public void setPhi(int phi) { this.phi = phi; } public int getEng() { return eng; } public void setEng(int eng) { this.eng = eng; } public int getComp() { return comp; } public void setComp(int comp) { this.comp = comp; } public Student(String name, String sex, int age, long number, int phi, int eng, int comp) { super(name, sex, age); this.number = number; this.phi = phi; this.eng = eng; this.comp = comp; } public double aver(){ return (phi eng comp)/3; } public int max(){ return Math.max(Math.max(phi, eng), comp); } public int min(){ return Math.min(Math.min(phi, eng), comp); } public String toString(){ return null; } } //测试程序 public class test { public static void main(String args[]){ Student s = new Student("李丽","女",18,200501,80,95,85); System.out.print("学号：" s.getNumber()); System.out.print("姓名：" s.getName()); System.out.print("性别：" s.getSex()); System.out.print("年龄：" s.getAge()); System.out.print("平均分：" s.aver()); System.out.print("最高分：" s.max()); System.out.print("最低分：" s.min()); } }

c语言，，!x与x!分别表示什么意思

C语言中只有!x没有x!。

!x的意思就是x!=0；当X=0时执行while循环；

！即取反，当x！=0时不执行；若x=0，则!x非零；

若x不等于零，则!x=0；一般用if(!x)来做判断式。