#include<iostream.h>
class student
{
private:
    int number,grade;
    char name[20];
public:
    student(int num,int gra,char na[20])
    {number=num;
    grade=gra;
    name[20]=na[20];}
    void out(int num,int gra,char na[20])
    {cout<<"姓名:"<<na<<"学号:"<<num<<"成绩:"<<gra<<endl;}
    friend int compare(student &s1,student &s2);
};
int compare(student &s1,student &s2)
{
    if(s1.grade>s2.grade)
        cout<<"The better:"<<"姓名:"<<s1.name<<"学号:"<<s1.number<<"成绩:"<<s1.grade<<endl;
    else
        cout<<"The better:"<<"姓名:"<<s2.name<<"学号:"<<s2.number<<"成绩:"<<s2.grade<<endl;
    return 0;
}
int main()
{
    student s1(1,76,"Jane"),s2(2,81,"Jack");
    s1.out(1,76,"Jane");
    s2.out(2,81,"Jack");
    int compare(s1,s2);
    return 0;
}
Int 类型不对，该换什么

你这个只是做了比较然后输出其实不需要返回值返回void把return 0去掉，你的out函数不需要参数，直接用数据成员就行了

调用时把返回类型int去掉

#include<iostream>
#include<string>
using namespace std;
class student
{
private:
    int number,grade;
    string name;
public:
    student(int num,int gra,string na)
    {number=num;
    grade=gra;
    name=na;}
    void out(int num,int gra,string na)
    {cout<<"姓名:"<<na<<"学号:"<<num<<"成绩:"<<gra<<endl;}
    friend void compare(student &s1,student &s2);
};
void compare(student &s1,student &s2)
{
    if(s1.grade>s2.grade)
        cout<<"The better:"<<"姓名:"<<s1.name<<"学号:"<<s1.number<<"成绩:"<<s1.grade<<endl;
    else
        cout<<"The better:"<<"姓名:"<<s2.name<<"学号:"<<s2.number<<"成绩:"<<s2.grade<<endl;
}
int main()
{
    student s1(1,76,"Jane"),s2(2,81,"Jack");
    s1.out(1,76,"Jane");
    s2.out(2,81,"Jack");
    void compare(student s1,student s2);
    return 0;
}

[ 本帖最后由 hzj199603 于 2015-5-12 18:37 编辑 ]

多谢

多谢，