Need help about string

Hello,this is my code.

here is the output.

http://img201.imageshack.us/img201/5564/cppqt3.jpg

the problem is,
the output must look like this.

========================
Group :

Group :
========================

this mean,user can insert 2 groups.

example :

========================
Group : Group A

Group : Group B
========================

and the program will save the group name as a file.

Can some one fix this code ?

Code:

#include <iostream>
#include <conio.h>
#include <string>
#include <fstream>

using namespace std;

int main ()
{
    
    char groupname[300];
    int numGroups;
    
    cout<<"How many groups do you wish to create?"<<endl;
    cin>>numGroups;
    
    for(int i=0;i<numGroups;i++)
    {
            cout << "Group : ";
            cin.getline(groupname,30);
            
            ofstream group;
            ofstream (groupname, ios::out);
    }
  
  getch();
  return 0;
}

the first time you pressed return after the number, the "cin>>numGroups" only retrieves the number, and the newline stays in there

so the next time you call cin.getline(groupname,30), it retrieves an empty line

A common solution is to add cin.ignore() immediately after the call to cin>>numGroups to ignore the <enter> typed by the user.

Note that you #included <string> but you are not using the C++ string class. Unless you have a good reason, you should prefer C++ strings over the C style character arrays you are using.

OK,
I already fix it.
the code is working but i got a problem with the file output.

let say the file name is like this :

example :

========================
Group : test1

Group : test2
========================

when i checked in the folder,2 files has been created.

check this screenshot

http://img187.imageshack.us/img187/1264/cpp2qn6.jpg


1 file is === test1
another file is == est2

the problem is, why "G" is missing for Group B ?

maybe anyone can fix my code or give me some idea.

No idea, show us the code, not your output.

Code:

    char groupname[300];
    int numGroups;
    
    cout<<"How many groups do you wish to create?"<<endl;
    cin>>numGroups;
    
    for(int i=0;i<numGroups;i++)
    {
            cout << "Group Name : ";
            cin.ignore();
            cin.getline(groupname,30);
            
            ofstream group;
            ofstream (groupname, ios::out);
    }

> cin.ignore();
This is great at removing the trailing junk from cin>>numGroups; but on the 2nd iteration, it removes the first char of each line of input.

Maybe do this once, before entering the loop?

HOho man...thats great....it is working now !

Code:

using namespace std;
  
string groupname;
int numGroups;
ofstream group;
    
cout<<"How many groups do you wish to create?"<<endl;
cin>>numGroups;
cin.ignore();
    
for(int i=0;i<numGroups;i++)
    {
            cout << "Group Name : ";
            if(getline(cin,groupname).gcount() > 30)
                {
                   cout << "No more than 30 characters, please." << endl;
                   i--;
                   continue;
                }

            group.open(groupname.c_str());
            group.close();
    }

>> std::string groupname;
Using a C++ string instead of C style strings is an improvement.

>> cout << "No more than 30 characters, please." << endl;
I don't think the check for 30 characters is necessary, though, as it was almost certainly only originally needed to avoid overstepping the character array bounds.

>> if(std::getline(cin,groupname) > 30)
This won't work, getline does not return the number of characters read. As I mentioned above, the > 30 is probably not necessary anyway, so if(std::getline(cin,groupname)) should be good.

>> ofstream group;
Moving a variable to a larger scope unnecessarily is not an improvement, IMO. There will be no noticeable performance benefits, and keeping the variable scope limited is better design here.

>> group.close();
You would also want to clear() any failbits at the end of the loop just in case, although this would be more likely to cause a problem on an input file. Of course, moving the variable declaration back inside the for loop scope would make the close() automatic and a clear() unnecessary.

>> group.open(groupname);
This should be group.open(groupname.c_str()); since filestreams take C style strings as arguments to open.

It seems you replied to my code as I was editing it. Anyway, all of your comments did apply.

Hello,
why when i inserted group name without space,the program suddenly quit.

here is my code

Code:

#include<iostream>
#include<string>
#include<fstream>
#include<conio.h>

using namespace std;

int main()
{
    cout<<"How many groups?"<<endl;
    int nGroup;
    cin>>nGroup;
    
    string delGroup;
    string delTeams;
        

    for(int i=0;i<nGroup;i++)
    {
        cout<<"What name for Group "<<i+1<<"?"<<endl;

        char GrpName[300];
      
        fflush(stdin);
        
        cin.getline(GrpName,30);
        string FileName=GrpName;
        //create a string to delete the Group file
        string copyFileName=FileName;
        int indexGroup=copyFileName.find_first_of(' ');
        copyFileName.erase(indexGroup);
        delGroup="del "+copyFileName+"*";
        fstream Group(FileName.c_str(), ios_base::in);// attempt open for read
        if (!Group)
        {
            // file doesn't exist; create a new one
            Group.open(FileName.c_str(), ios::out|ios::binary|ios::app);

            cout<<"Lets input team names..."<<endl;
            cout<<"How many teams?"<<endl;
            int nTeam;
            cin>>nTeam;

            for(int j=0;j<nTeam;j++)
            {
                cout<<"What name for team "<<j+1<<"?"<<endl;
                
                char TeamName[300];
                
                fflush(stdin);
                cin.getline(TeamName,30);
                Group<<TeamName<<"\n";
                
                string sTeam=TeamName;
                //create a string to delete the team file and team extended files
                string copysTeam=sTeam;
                int indexTeam=copysTeam.find_first_of(' ');
                copysTeam.erase(indexTeam);
                delTeams="del "+copysTeam+"*";

                string sTeamEx=sTeam + "ex";
                
                fstream Team(sTeam.c_str(), ios_base::in);// attempt open for read
                if (!Team)
                {
                    // Team doesn't exist; create a new one
                    Team.open(sTeam.c_str(), ios::out|ios::binary|ios::app); 
                    Team.close();
                }
                else //ok, Team exists; error message
                {
                    cout<<"ERROR, the Team already exists"<<endl;
                }
                
                fstream TeamEx(sTeamEx.c_str(), ios_base::in);// attempt open for read
                if (!TeamEx)
                {
                    // Team Extended doesn't exist; create a new one
                    TeamEx.open(sTeamEx.c_str(), ios::out|ios::binary|ios::app); 
                    TeamEx.close();
                }
                else //ok, Team Extended exists; error message
                {
                    cout<<"ERROR, the Team Extended already exists"<<endl;
                }

            }
            Group.close();            
        }
        else //ok, group exists; show the error message
        {
            cout<<"ERROR, the group already exists"<<endl;
        }         
    }
    cout<<"Do you want to clean up all files created ?(y/n)"<<endl;
    char YesNo[1];
    cin>>YesNo[0];
    if(YesNo[0]=='y'||YesNo[0]=='Y')
    {
        cout<<"deleting all files created"<<endl;
        cout<<"deleting Group files..."<<endl;
        system(delGroup.c_str());
        cout<<"deleting Team files and Team Extended files..."<<endl;
        system(delTeams.c_str());
    }
    
    getch();
    return 0;
}

let say group name --> GroupA
result --> program suddenly quit

let say group name --> Group A
result --> the program continue

why is this happened ?

>> why when i inserted group name without space,the program suddenly quit.
Maybe because your code looks for the first space in the group name when it uses the code:

Code:

int indexTeam=copysTeam.find_first_of(' ');

But if there is no space that will return -1. You then call erase with -1 as an argument, which might be crashing the program. YOu should compare indexTeam with string::npos, and only erase if they is not equal.

>> fflush(stdin);
Why is this there? Besides being bad practice in C, there is no reason to use it in C++. The first fix suggested, adding cin.ignore() after the call to cin>>nGroup; is the better way to go.

fflush(stdin);

the function is same with cin.ignore()

i still have no idea to use string::npos

maybe someone can show me some example.

>> the function is same with cin.ignore()
No, it is not the same. Use cin.ignore().

>> i still have no idea to use string::npos
Do you know how to compare two values in an if statement? Make an if statement that compares indexTeam and string::npos and enters the if block if those two values are not equal. How would you do it if I said to compare indexTeam to -1? The code would be the same except you'd replace -1 with string::npos.