Having difficulty creating and using classes.

[samimmu]

actually i have a lot of problems with code down. i actually i made this code to let create a file for several student, i tried by my name but unfortunately i got alot of errors i don't know how can i debug them. if anyone of you know how to complete the program by making the user to enter so many student and their marks and let the user to make some modification or edit his or her names, i want at least 100 student to enter their names, ids,marks, and display the name, the id,the avarage marks for each student in files,this is the code,
i wish i can get a complete program. please help me and thank you, it is really important, i am really thankful for all of you,have a great time guys

#include<iostream>
#include<fstream>
using namespace std;
const int SIZE=100;
 class Info{
       private:
               string id;
               double mark;
 
 
       public:
           Info();
           void display();
            void getData(); 
            void setMark(double); // change the value.
            double getMark(); // assest the value
             string getName();
 
};
 
Info:: Info(){
       id=" ";
       mark=0;
       }
       void Info:: getData(){
            cout<<" please enter the student id:"<<endl;
            getline(cin,id);
            cout<<" please enter the student mark:"<<endl;
            cin>> mark;
            std:: cin.ignore();
            }
 void Info:: display(){
   cout<<id<< "\t"<< mark << endl;
 
}   
void Info::setMark(double m){
     mark=m;
     }
     double Info::getMark(){
            return mark;
            }
           void save(Info s[], int SIZE){
                 ofstream myfile;
                 myfile.open("mark.sami");
                 for( int i=0; i<SIZE; i++)
                 myfile<< s[i].getName <<"\t"<<s[i].mark<<endl<<endl;;
            myfile.close();
            }
             void load(){
                  string line;
                  ifstream myfile("mark.sami");
                  if(myfile.is_open())
                  {
                                      while(! myfile.eof())
                                      {
                                              getline(myfile,line);
                                              cout<<line<< endl;
                                              }
                                              myfile.close();
                                              }
                                              else cout<< " Unable to open file"<<endl;
                                              }    
 
 int main()
 {
    Info std[SIZE];
    for(int i=0; i<SIZE; i++)
     std[i].getData();
     cout<<" \nName\tmark"<<endl;
     cout<<"=========================="<<endl;
    // load();
   for(int i=0; i<SIZE; i++)
    std[i].display();
    save(std,SIZE);
 
     return 0;
     }

[sicarie]

What are the errors you are getting? Can you copy and paste them here as well?

[samimmu]

if u don't mind, u can copy and paste the code and compile it, actually i didn't know how to create a file for each students, i think the errors is ,"Double Marks is private" i really don't know what does it mean, i tried to change to other types but still the same errors, still so weak in designing a programs because i have not learn classes in deep

[sicarie]

if u don't mind, u can copy and paste the code and compile it, actually i didn't know how to create a file for each students, i think the errors is ,"Double Marks is private" i really don't know what does it mean, i tried to change to other types but still the same errors, still so weak in designing a programs because i have not learn classes in deep

I can, but I would like you to look at the errors - my goal here is not just to fix your program, but help you be able to diagnose a similar issue in the future, hopefully make you a better and more independent programmer (and then you can come back and maybe even help me!).

[nirJianWu]

there're some errors just because you forgot to include a header file <string>

for example, when you compile your code, you'll get a error hint that getline() function does not take one argument, but you do offer it two arguments, with a ifstream myfile and a string line.

why does compiler consider you just give it only one argument?

It's because that you declare the variable "line" by using "string line" but you don't tell compiler what the string is by including <string>.

By the by, I use VS2005, maybe some other compilers can recognise it without <string> header file... I don't make a test.

Moreover, please pay attention to this line
"myfile<< s[i].getName <<"\t"<<s[i].mark<<endl<<endl;;"

you wanna get the s[i]'s name via a function named getName, so when you call that function, you should write it as "s[i].getName()". Do not forget the parentheses, without them the compiler would take getName a variable of s[i], other than a member function.

Another problem is, you wanna get s[i]'s mark via a directly visit, however, the member mark in your Info class is defined private, which means you cannot visit it directly or it's invisable to you, the only way you get it is using the interface you defined in your Info class, "getMark()".

[samimmu]

I can, but I would like you to look at the errors - my goal here is not just to fix your program, but help you be able to diagnose a similar issue in the future, hopefully make you a better and more independent programmer (and then you can come back and maybe even help me!).

thank you Sicarie. actually i am a new programmer and i have learned classes in deep, i just read from book and that question i posted is my exercise, i tried it out and did the best i could but i got the bugs actually i don't how to use " double mark") it is private, i don't know how to deal with it. hopefully u can help me out, thank you so much.

[samimmu]

thank thank thank you so much. it is really working, thank you so much, but one more thing if u don't mind, how can i get the avarage months for each students and make a file for each a students, your help is highly appreciated, thank you so much, but in the program it can not create a file, how i do that?

[samimmu]

thank you so much, but u know i still have a problem of creating a file for each student and display the average marks for each one in file .i wish u help out to figure this problem.

there're some errors just because you forgot to include a header file <string>

for example, when you compile your code, you'll get a error hint that getline() function does not take one argument, but you do offer it two arguments, with a ifstream myfile and a string line.

why does compiler consider you just give it only one argument?

It's because that you declare the variable "line" by using "string line" but you don't tell compiler what the string is by including <string>.

By the by, I use VS2005, maybe some other compilers can recognise it without <string> header file... I don't make a test.

Moreover, please pay attention to this line
"myfile<< s[i].getName <<"\t"<<s[i].mark<<endl<<endl;;"

you wanna get the s[i]'s name via a function named getName, so when you call that function, you should write it as "s[i].getName()". Do not forget the parentheses, without them the compiler would take getName a variable of s[i], other than a member function.

Another problem is, you wanna get s[i]'s mark via a directly visit, however, the member mark in your Info class is defined private, which means you cannot visit it directly or it's invisable to you, the only way you get it is using the interface you defined in your Info class, "getMark()".

[nirJianWu]

thank you so much, but u know i still have a problem of creating a file for each student and display the average marks for each one in file .i wish u help out to figure this problem.

ur.. I dont understand your requirement very much:(

will u please show me a more specific example showing your requirement?

regards..

[sicarie]

thank you so much, but u know i still have a problem of creating a file for each student and display the average marks for each one in file .i wish u help out to figure this problem.

Do you have a list of the students beforehand? Otherwise, you'll have to create these files dynamically, which can get interesting.

Off the top of my head, I'd recommend creating an array of strings, and then filling that with the names, then when you create the outfiles for the individual students, you can use those strings as the names of the files. I'd also recommend using strcpy() or another of the functions here to tack on the absolute file location, otherwise you'll have to find where the file was created. That's easy enough with the search function, but it's easier to just put them in a directory that's easy to access.

[samimmu]

ur.. I dont understand your requirement very much:(

will u please show me a more specific example showing your requirement?

regards..

thank you, actually my requirement is to create a file for 100 students and display in the file the avarage marks for each student and his name,and make the the user to edit some of his informations

[sicarie]

thank you, actually my requirement is to create a file for 100 students and display in the file the avarage marks for each student and his name,and make the the user to edit some of his informations

So just one file, correct? You can use an fstream (google c++ file io or c file io), and that will create the file.

[samimmu]

So just one file, correct? You can use an fstream (google c++ file io or c file io), and that will create the file.

[ i need more than one file. i have 100 students, so i need to create a file for each one of them which can show their names,avarages marks,] thank you so much

Regards

Alkindi

[sicarie]

[ i need more than one file. i have 100 students, so i need to create a file for each one of them which can show their names,avarages marks,] thank you so much

Regards

Alkindi

Then yeah, my post #10 would be the way I would approach the problem.

[samimmu]

i wish u can get my wants or requirement, actually here i can not create a file and cin the information for each students, i want the size to 100, but unfortunately i can not use the for loop

#include<iostream>
#include<fstream>
#include<string>
#include<iomanip>
using namespace std;

const int size=10;
int main()
{

ifstream inFile;
ofstream outFile;

int quiz1, quiz2, quiz3, quiz4, quiz5;
double average;
char studentId;
inFile.open("a:\\quiz.txt");
outFile.open("a:\\quizavg.out");


// for(int i=0 ; i< size; i++)
cout<<" the students information"<<endl;
inFile>>studentId;
outFile<<" student ID: "<< studentId<< endl;
inFile>> quiz1>>quiz2>> quiz3>> quiz4>> quiz5;
outFile<<" Quize scores:"<< setw(4)<< quiz1
<< setw(4)<< quiz2<< setw(4)<< quiz3<< setw(4)<< quiz4
<<setw(4)<<quiz5<< endl;

average= static_cast<double>(quiz1+quiz2+quiz3+quiz4+quiz5)/5.0;
outFile<< " Average test score:"<< setw(6)<< average<< endl;


inFile.close();
outFile.close();
system("pause");
return 0;
}

[sicarie]

i wish u can get my wants or requirement, actually here i can not create a file and cin the information for each students, i want the size to 100, but unfortunately i can not use the for loop

#include<iostream>
#include<fstream>
#include<string>
#include<iomanip>
using namespace std;

const int size=10;
int main()
{

ifstream inFile;
ofstream outFile;

int quiz1, quiz2, quiz3, quiz4, quiz5;
double average;
char studentId;
inFile.open("a:\\quiz.txt");
outFile.open("a:\\quizavg.out");


// for(int i=0 ; i< size; i++)
cout<<" the students information"<<endl;
inFile>>studentId;
outFile<<" student ID: "<< studentId<< endl;
inFile>> quiz1>>quiz2>> quiz3>> quiz4>> quiz5;
outFile<<" Quize scores:"<< setw(4)<< quiz1
<< setw(4)<< quiz2<< setw(4)<< quiz3<< setw(4)<< quiz4
<<setw(4)<<quiz5<< endl;

average= static_cast<double>(quiz1+quiz2+quiz3+quiz4+quiz5)/5.0;
outFile<< " Average test score:"<< setw(6)<< average<< endl;


inFile.close();
outFile.close();
system("pause");
return 0;
}

The A:\ drive is usually recognized as 'floppy disk,' are you trying to write to a floppy, or your hard drive? It's possible that the letter was assigned to a local drive, but I'd check that out. (C is usually the hard disk)

If you can't use a for loop, why not use one of the other loops to mimick a for loop? Such as while counter < 100 do stuff, and increment counter. Or if counter < 100, dostuff, increment counter.

At first glance, your files look like they're declared properly (unless there's no floppy in there...).