Grade book program using arrays and Bubble sort (many problems)

[xtheendx]

I am writing a gradbook type program. It first allows the user to enter the number of students they want to enter. then allows them to enter the first name, last name, and grade of each student. The program then should sort the names alphabetically by last name and display a list of all the students names and grades in alphabetical order. I have completed all my functions and classes, but i am getting a god aweful amount of errors and i am not sure what is wrong. It is my first attempt at using classes and objects and bubble sort so i am not sure. here is my code let me know any problems you see, i would greatly appreciate some guidance. First is the header file

#include <iostream>  // allows the program to output data to the screen
 
// students class definition
class students
{
public:
    int arraySize; // size of array entered by user for number of students
 
    int getNumstudents(int arraySize); // function to get the number of students user wants to enter
    void getData(int arraySize); // function to get first and last name and the students grade
    void displayMessage(); // displays welcome message
    void sortData (); // function to alphabetize by last name using buble sort
    void printData (); // function to print data
private:
    char*firstName[arraySize]; // array of students first names
    char*lastName[arraySize]; // array of students last names
    int grades[arraySize]; // array of students grades
};
 

and here is the cpp file

 #include <iostream>  // allows the program to output data to the screen
#include <conio.h>
#include  <iomanip>
#include <cstdlib>
#include <string.h>
#include "students.h" // gradebook class defintion
 
 
using std::cout; // program uses cout
using std::cin; // program uses cin
using std::endl; // program uses endl
using std::setprecision; // set numeric output precision
using std::fixed; // ensures that decimal point is displayed
using std::setw;
 
 
void  students::displayMessage()
{
 
    cout << "Welcome to the Student Scores Application." << endl;
}
 
// sorts data alphabetically by last name using bubble sort    
void students::sortData()
{
 
    for(int i = 0; i < arraySize ; i++){
            for(int j = i+1; i < arraySize; j++){
                  if(strcmp(lastName[i]){
                    char *temp = lastName[i];    // swap pointers
                    lastName[i] = lastName[j];
                    lastName[j] = temp;
                }
              }
        }
 }
 
// Prints all the students data
void students::printData()
{
 
    for (int i = 0; i < arraySize; i++)
    {
 
    cout << "Student " << num << " last name: " << lastName[i] <<", " << firstName[i] << ": " << grades[i] << endl;
 
    }
}
 
// gets the number of students the user wnats to enter and sets that as the arraysize
int students::getNumstudents(int arraySize)
{
    cout << "Enter number of students to enter: ";
    cin >> arraySize;
}
 
// gets students info from user
void students::getData(int arraysize)
{
    int num = 1;
    char*userinput1;
    char*userinput2;
    int userinput3;
 
    while ( num <= arraySize){
 
    cout << "Student " << num << " last name: ";
 
    lastName[arraysize] = userinput1;
 
    cout << "Student " << num << " first name: ";
 
    firstName[arraysize] = userinput2;
 
    cout << "Student " << num << " score: ";
 
    grades[arraysize] = userinput3;
 
    num++
    }
}
 
// function main begins program exectuion
int main() 
{
 
 
    students.displayMessage();
 
    students.getNumstudents();
 
    students.getData();    
 
    students.sortData();
 
    students.printData();
}
 

[Ganon11]

Two things I immediately notice:

1) This is C++ (as I see from you using strings, cin, cout, etc.), so why are you using char* to hold names and such? That's what std::strings are for.

2) In your main(), you are trying to call methods on an object, but you haven't made a student object. You need to say:

student myStudent;
 
myStudent.displayMessage();

or something of the sort.

In addition, I'm not sure your design is entirely straightforward . A student shouldn't have to know how many classmates he/she has (i.e. the array size), nor should he/she need to have information about inputting/outputting information (getData(), displayMessage( )).

An easier to design (not to mention easier to work with) design would be like this: the Student class has a first name and last name as well as an array/vector of grades, and a constructor which allows you to set these attributes. Then you either have another class, maybe Class, which will hold a collection of students and can sort them, etc.

Finally, if you are getting errors, it's usually easier to go ahead and post these errors as well, rather than letting repliers blindly try to analyze your code.

[xtheendx]

thanks for the help man, i got rid of all the errors and the program "runs' now. When it runs it just prints out getData() cout stuff 100 times, and then prints out Student Last name: folloed by a bunch of jibberish. The program requirments call for the program to promt the user for the number of students they would like to enter, that is the only reason i did it like that. I have commened out the bubble sort, becaussei can't figure out how to make it sort the last names. Any help with with getting the program working better would be apprecriated. here is what i have now,

 
#include <iostream>  // allows the program to output data to the screen
#include <string.h>
 
// students class definition
class students
{
public:
    int getNumstudents(); // function to get the number of students user wants to enter
    void getData(); // function to get first and last name and the students grade
    void displayMessage(); // displays welcome message
    //void sortData (); // function to alphabetize by last name using buble sort
    void printData (); // function to print data
    const static int numStudents = 100;
private:
    char firstName[100]; // array of students first names
    char lastName[100]; // array of students last names
    int grades[100]; // array of students grades
};
 

 /* 
Josh Mauney
CSC215
4-28-08
student grade program
project 2
*/
 
#include <iostream>  // allows the program to output data to the screen
#include <conio.h>
#include  <iomanip>
#include <cstdlib>
#include <string.h>
#include "students.h" // gradebook class defintion
 
 
using std::cout; // program uses cout
using std::cin; // program uses cin
using std::endl; // program uses endl
using std::setprecision; // set numeric output precision
using std::fixed; // ensures that decimal point is displayed
using std::setw;
using std::string;
 
 
void  students::displayMessage()
{
 
    cout << "Welcome to the Student Scores Application." << endl;
}
 
// sorts data alphabetically by last name using bubble sort    
/*void students::sortData(int numStudents)
{
    char temp[100];
 
    for(int i = 0; i < numStudents ; i++){
            for(int j = i+1; i < numStudents; j++){
                  if(strcmp(lastName[i], lastName[j] > 0)){
                    temp = lastName[i];    
                    lastName[i] = lastName[j];
                    lastName[j] = temp;
                }
              }
        }
 }
*/
// Prints all the students data
void students::printData()
{
 
 
    for (int i = 0; i < numStudents; i++)
    {
 
    cout << "Student last name: " << lastName[i] <<", " << firstName[i] << ": " << grades[i] << endl;
 
    }
}
 
// gets the number of students the user wnats to enter and sets that as the arraysize
int students::getNumstudents()
{
    int arraySize;
    cout << "Enter number of students to enter: ";
    return arraySize;
}
 
// gets students info from user
void students::getData()
{
    int num = 1;
    char userinput1;
    char userinput2;
    int userinput3;
 
    while ( num <= numStudents){
 
    cout << "Student " << num << " last name: ";
 
    lastName[numStudents] = userinput1;
 
    cout << "Student " << num << " first name: ";
 
    firstName[numStudents] = userinput2;
 
    cout << "Student " << num << " score: ";
 
    grades[numStudents] = userinput3;
 
    num++;
    }
}
 
// function main begins program exectuion
int main() 
{
    students mystudent;
 
    mystudent.displayMessage();
 
    mystudent.getNumstudents();
 
    mystudent.getData();    
 
    //mystudent.sortData();
 
    mystudent.printData();
 
    char pause = getchar();  // program pauses before ending
 
    getchar();
} 

[oler1s]

Quick note: it's <string>, not <string.h> . You do know how standard headers work, do you not?

So, what have you done to figure out where the problem areas are? It's not nice to take your non working program, dump it on us, and say "figure out what's wrong please".

[xtheendx]

I'm sorry that is not what i have meant to do...I just wanted suggestions and i got some that helped alot.. like the idea of using strings, so now i am using string vectors and completly redid my program. I do appreicate your guys help and sorry if came off stupid...i was just really lost.. it being my first large program and all. Here is what i have now as sort of prototype using the vectors. I can get it to read the names i eneter, but for some reason as soon as i am done enetering them the program quits instead of displaying them.

#include <iostream>  // allows the program to output data to the screen
#include <string>
 
// students class definition
class students
{
public:
    void getData(); // function to get first and last name and the students grade
    void displayMessage(); // displays welcome message
 
private:
 
}; 

 #include <iostream>  // allows the program to output data to the screen
#include <conio.h>
#include  <iomanip>
#include <cstdlib>
#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include "students.h" // gradebook class defintion
 
 
using std::cout; // program uses cout
using std::cin; // program uses cin
using std::endl; // program uses endl
using std::setprecision; // set numeric output precision
using std::fixed; // ensures that decimal point is displayed
using std::setw;
using std::string;
using std::vector;
 
 
void  students::displayMessage()
{
 
    cout << "Welcome to the Student Scores Application." << endl << endl;
}
 
 
void students::getData()
{
    int numStudents;
    vector<string> student_names(numStudents);
 
    cout <<"Enter number of students to enter: ";
    cin >> numStudents;
 
    for (int i = 0; i <= numStudents; i++)
    { 
            cout << "Enter student name (Enter to finish): "; 
            getline (cin, student_names[i]);
    }
 
            // sort them alphabetically
        sort (student_names.begin(), student_names.end());
 
    for (int i =0; i < numStudents; i++)
    {
            cout << student_names[i];
    }
 
 
 
}
 
// function main begins program exectuion
int main() 
{
    students mystudent;
 
    mystudent.displayMessage();
 
    mystudent.getData();    
 
}

[oler1s]

I have two questions for you. Hopefully this gives you a hint.

int i = 0; i <= numStudents

You sure about that?

Next. Look at the following code:

void createNumbers()
{
    std::vector<int> numbers;
    numbers.push_back(1);
    numbers.push_back(3);
    numbers.push_back(10);
}
 
void printNumbers()
{
    createNumbers();
    std::cout << numbers[0] << std::endl;
}
 

What's wrong with the above code?

[xtheendx]

I have two questions for you. Hopefully this gives you a hint.

You sure about that?

Next. Look at the following code:

void createNumbers()
{
    std::vector<int> numbers;
    numbers.push_back(1);
    numbers.push_back(3);
    numbers.push_back(10);
}
 
void printNumbers()
{
    createNumbers();
    std::cout << numbers[0] << std::endl;
}
 

What's wrong with the above code?

the only problem i can see is that your just print the 0 space in the numbers array. So i am guessing that is what i am doing in my code..calling it to output nothing. and as far as being sure about i=0; i < numStudents; i++...i am pretty sure because that would call each array element 0 thorugh the size of array. right? i appreciate your method of help...i don't like being told the answer. thanks

[oler1s]

You've missed both hints, so I'll throw it again in a slightly more indepth fashion. Let's start with the <= numStudents issue. I'll throw out sample code again.

int numItems = 1;
std::vector<int> numbers(numItems);
numbers[0] = 50;
 

How many elements are there in numbers? Clearly 1. Let's loop over this vector.

for (int i=0; i<=numItems; ++i) //remember that numItems=1
{
    std::cout << numbers[i] << std::endl;
}
 

Write this out by hand. Write down i. Write down the evaluation of i<= numItems. If true, write down numbers[i]. Then repeat the loop. You'll see the problem (a very, very frequent one).

As to my second example. You also missed the issue.

the only problem i can see is that your just print the 0 space in the numbers array

Terminology first. It's a vector, not an array. There is no such thing as a 0 space. An index of 0 gets me the first element. Also, it's impossible to output, but have nothing as your output. You either output or you don't. If you do output, it must be something in memory. Now, you know that the computer works in 1s and 0s. That is, you either have a 1 or 0. "Nothing" is not a part of the binary system. But this all gets away from the real important point.

First, answer this question.

#include <iostream>
 
int main()
{
    std::cout << i;
}
 

What's wrong here?

Then:

#include <iostream>
 
void someFunc()
{
    int i=50;
}
 
int main()
{
    std::cout << i;
}
 

What's wrong here?

Then:

#include <iostream>
 
void someFunc()
{
    int i=50;
}
 
int main()
{
    someFunc();
    std::cout << i;
}
 

So what's wrong here? Don't hesitate to use your compiler to get a hint.

[xtheendx]

You've missed both hints, so I'll throw it again in a slightly more indepth fashion. Let's start with the <= numStudents issue. I'll throw out sample code again.

int numItems = 1;
std::vector<int> numbers(numItems);
numbers[0] = 50;
 

How many elements are there in numbers? Clearly 1. Let's loop over this vector.

for (int i=0; i<=numItems; ++i) //remember that numItems=1
{
    std::cout << numbers[i] << std::endl;
}
 

Write this out by hand. Write down i. Write down the evaluation of i<= numItems. If true, write down numbers[i]. Then repeat the loop. You'll see the problem (a very, very frequent one).

As to my second example. You also missed the issue.

Terminology first. It's a vector, not an array. There is no such thing as a 0 space. An index of 0 gets me the first element. Also, it's impossible to output, but have nothing as your output. You either output or you don't. If you do output, it must be something in memory. Now, you know that the computer works in 1s and 0s. That is, you either have a 1 or 0. "Nothing" is not a part of the binary system. But this all gets away from the real important point.

First, answer this question.

#include <iostream>
 
int main()
{
    std::cout << i;
}
 

What's wrong here?

Then:

#include <iostream>
 
void someFunc()
{
    int i=50;
}
 
int main()
{
    std::cout << i;
}
 

What's wrong here?

Then:

#include <iostream>
 
void someFunc()
{
    int i=50;
}
 
int main()
{
    someFunc();
    std::cout << i;
}
 

So what's wrong here? Don't hesitate to use your compiler to get a hint.

Alright on the first one the for loop is only ran through once when i=0, after that i = 1 and and so is numItems. So i see why that is wrong, but in my code i have declared int numStudents and then let the user define the number of students. So in my for loop i shouldn't have that problem...at least that is what i think.

And for the second questions on the codes you wrote, on all three of them you haven't declared i. But in my code i have declared i in the for loop. Maybe i am missing the big picture here. i will coninue to try to figure it out. I appreciate the help...i am sure it will click soon enough,

[xtheendx]

Alright i think i just had a revalation. i realized what you were saying about i < numStudents. I need to set it up so i is less than or equal to the size of the vector. so this is how i changed my code... and it worked it printed the names in alphbetical order.

 void students::getData()
{
    int numStudents;
    vector<string> student_names(numStudents);
 
    cout <<"Enter number of students to enter: ";
    cin >> numStudents;
 
    for (int i = 0; i <= numStudents; i++)
    { 
            cout << "Enter student name (Enter to finish): "; 
            getline (cin, student_names[i]);
    }
 
            // sort them alphabetically
        sort (student_names.begin(), student_names.end());
 
    for (int i =0; i <= student_names.size(); i++)
    {
            cout << student_names[i];
    }
 
 
 
} 

thanks for the help...hopefull y i will be ok from here on out....I know it is printing out right, but did i do it correctly, i jst want to make sure i am learning properly. thanks very much