2 edward liang Edward_Liang 于 2013.08.19 17:24 提问

初学C++中类的使用,求助

初学类的使用,在Accelerated C++上遇到编程题目如下:
编写一个类以及相关的函数以为学生产生成绩,用P/F表示成绩
假设只根据期中和期末成绩来计算,而且,如果一个学生的平均考试分数大于等于60的话,那这个学生及格
输出时列出学生姓名并列出相应的成绩,成绩用P/F表示
从data.txt读入成绩信息,将成绩输出到result.txt

data.txt截图如下:
CSDN移动问答

以下是我的代码:
#include
#include
#include
#include
#include
#include
#include
#include

using namespace std;

class Student_Info
{
private:
string name;
int mid,final;
public:
Student_Info(): name(" "),mid(0),final(0){}; //默认构造函数
Student_Info(string s,int x,int y);

~Student_Info(){}

void input(string s, int x, int y); //读入学生成绩数据
inline string output_name(){return name;} //输出学生姓名
inline bool pass(){return ((mid+final)>=60)?1:0;} //判断是否及格
};

void Student_Info::input(string s,int x,int y)
{
name=s;
mid=x;
final=y;
}

Student_Info::Student_Info(string s,int x,int y)
{
input(s,x,y);
}

char grade(Student_Info student)
{
return student.pass()?'P':'F';
}

int string2int(string txt)
{
int num;
stringstream ss;
ss< ss>>num;
if(!ss.good())
{
cerr<<"转换失败!"<<endl;
exit(1);
}
return num;
}

int main()
{
vector students;
vector pass;
vector temp,names;
vector points;
string tmp,str;
int x,y,i=0,length=0;
Student_Info student;
ifstream fin("data.txt");
ofstream fout("result.txt");
getline(fin, tmp);
//cout< while(getline(fin,tmp))
{
istringstream stream(tmp);
while(stream>>str)
temp.push_back(str);
x=string2int(temp1);
y=string2int(temp[2]);
student.input(temp[0],x,y);
students.push_back(student);
pass.push_back(grade(student));
names.push_back(student.output_name());
temp.clear();
}
for(;i<names.size();i++)
{
if(length<names[i].size())
length=names[i].size();
}
length=max(length,12);
fout<<left<<setw(length)<<"学生姓名"<<"学生成绩"<<endl;
for(i=0;i<names.size();i++)
fout<<left<<setw(length)<<names[i]<<pass[i]<<endl;
fin.close();
fout.close();
system("pause");
return 0;
}

问题如下:
在运行时只会瞬间弹出空的控制台并且立即退出,生成一个空的result.txt文档;在文件中添加测试语句(如以上代码所示),无输出。
尝试逐语句调试,在main函数两处涉及Student_Info类变量的声明处发现类私有成员都没有按照默认构造函数初始化
请问这究竟是什么原因造成的?该如何修改?

1个回答

John_ToString
John_ToString   2015.12.24 15:44

#if 1
#include
#include
#include
#include

#include
using namespace std;
class Student_Info
{
private:
string name;
int mid, final;
public:
Student_Info() : name(" "), mid(0), final(0){}; //默认构造函数
Student_Info(string s, int x, int y);
~Student_Info(){}
void input(string s, int x, int y); //读入学生成绩数据
inline string output_name(){ return name; } //输出学生姓名
inline bool pass(){ return ((mid + final) >= 60) ? 1 : 0; } //判断是否及格
};
void Student_Info::input(string s, int x, int y)
{
name = s;
mid = x;
final = y;
}
Student_Info::Student_Info(string s, int x, int y)
{
input(s, x, y);
}
char grade(Student_Info student)
{
return student.pass() ? 'P' : 'F';
}
int string2int(string txt)
{
int num;
stringstream ss;
ss >> num;
if (!ss.good())
{
cerr << "转换失败!" << endl;
exit(1);
}
return num;
}

int max(int x, int y)
{
return x > y ? x : y;
}

int main()
{
vector students;
vector pass;
vector temp, names;
vector points;
string tmp, str;
int x, y, i = 0, length = 0;
Student_Info student;
ifstream fin("data.txt");
ofstream fout("result.txt");
getline(fin, tmp);
//cout< while(getline(fin,tmp))
{
istringstream stream(tmp);
while (stream >> str)
temp.push_back(str);
x = string2int(temp[1]);
y = string2int(temp[2]);
student.input(temp[0], x, y);
students.push_back(student);
pass.push_back(grade(student));
names.push_back(student.output_name());
temp.clear();
}
for (; i<names.size(); i++)
{
if (length<names[i].size())
length = names[i].size();
}
length = max(length, 12);
fout << left << setw(length) << "学生姓名" << "学生成绩" << endl;
for (i = 0; i<names.size(); i++)
fout << left << setw(length) << names[i] << pass[i] << endl;
fin.close();
fout.close();
system("pause");
return 0;
}
#endif

这是我修改后的代码...

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