文件操作
#include<iostream>
#include<fstream>
#include<iomanip>
using namespace std;

struct student
{
char name[10];
int num;
float score[3];
float avr;
}stud[5];

void main()
{
float sum;
int i,j;
cout << "input the information of five student!"<<endl;
for(i = 0;i < 5;i++)
{
cout << "name:";
cin >> stud[i].name;
cout << "num:";
cin >> stud[i].num;
for(j = 0;j < 3;j++)
{
cout << "score" << j+1 << ":";
cin >> stud[i].score[j];
sum += stud[i].score[j];
}
stud[i].avr = sum /3;
cout << endl;
}

ofstream outfile("stud.dat");
if(!outfile)
{
cout << "open error!" << endl;
abort();
}

outfile<<"name num socre1 score2 score3 average"<<endl;

for(i = 0;i < 5;i++)
{
outfile << stud[i].name << " " << stud[i].num << " ";
for(j = 0 ;j < 3;j++)
{
outfile << stud[i].score[j] << " ";
}　　　　　
outfile << stud[i].avr << endl;
}
outfile.close();
}
有五个学生，每个学生有3门课的成绩，从键盘输入以上数据（包括学生号，姓名，三门课成绩），
计算出平均成绩，况原有的数据和计算出的平均分数存放在磁盘文件"stud"中。*/
以上代码有啥错啊？？求助。。。。。。。。。

[解决办法]

C/C++ code

#include<iostream>#include<fstream>#include<iomanip>using namespace std;struct student{    char name[10];    int num;    float score[3];    float avr;}stud[5];void main(){    float sum;    int i,j;    cout << "input the information of five student!"<<endl;    for(i = 0;i < 5;i++)    {        cout << "name:";        cin >> stud[i].name;        cout << "num:";        cin >> stud[i].num;        for(j = 0;j < 3;j++)        {            cout << "score" << j+1 << ":";            cin >> stud[i].score[j];            sum += stud[i].score[j];        }        stud[i].avr = sum /3;        cout << endl;    }    ofstream outfile("stud.dat");    if(!outfile)    {        cout << "open error!" << endl;        abort();    }    outfile<<"name num socre1 score2 score3 average"<<endl;    for(i = 0;i < 5;i++)    {        outfile << stud[i].name << " " << stud[i].num << " ";        for(j = 0 ;j < 3;j++)        {            outfile << stud[i].score[j] << " ";        }        outfile << stud[i].avr << endl;    }    outfile.close(); }
[解决办法]
C/C++ code
第一点：sum没有初始化。就加能算对嘛！sum = 0;这是问题根源，不是ofstream的问题第二点：/除法。最好把3写成3.0第三点：用double安全些