getting memory errors on beginners progam

[Sevengraff]

using C++
The program compiles fine, but it will pop up a little window saying it "Generated Errors and must be closed by Windows. Also, how can i properrly pass the grade array into my function? I cant find my notes on how to do that.

here is my program. it takes input like so:
1 80 84 91
where its Student ID, Test1 score, Test2, Final Exam, then outputs things like student average score and stuff to output.txt

// 
// Nicholas Funnell
// Assignment #1
// january 29, 2003
// -------------------
// Takes data from input.txt, processes test scores and sends output to output.txt
//

#include <fstream>

using namespace std;

struct DATA
{
	// holds data about student that will be printed to output.txt
	int id;
	int average;
	int grade;
};

void GetStudentData ( DATA &student, ifstream &fin, int grade[5] )
{
	// *** GetStudentData() will get one line from the file opened by fin 
	// (we will open input.txt in main() ) Takes the values from the line and
    // puts them in a struct, and also computes the students average grade and
    // letter grade.

	int letter_grade, test1, test2, testFinal;
	
	fin >> student.id >> test1 >> test2 >> testFinal; // read in from file.
	student.average = int(0.20 * test1 + 0.30 * test2 + 0.50 * testFinal);
											// compute average semester grade
	
	// here we decide which letter grade student got
	if(student.average >= 90)
		letter_grade = 4;	// grade: A
	else if(student.average >= 80 && student.average <= 89)
		letter_grade = 3;	// grade: B
	else if(student.average >= 70 && student.average <= 79)
		letter_grade = 2;	// grade: C
	else if(student.average >= 60 && student.average <= 69)
		letter_grade = 1;	// grade: D
	else 
		letter_grade = 0;	// grade: F
	// now assign that grade to the student & update the count of that grade 
	student.grade = letter_grade;
	grade[letter_grade] += 1;       // keeping track of number of grades
	// end of function
	return;
}

void PrintStudentData ( DATA &student, ofstream &fout )
{
	char grade[5];	// letter grades.
	grade[0] = 'F';
	grade[1] = 'D';
	grade[2] = 'C';
	grade[3] = 'B';
	grade[4] = 'A';
	// print out the stuff on a student one line at a time...
	fout << student.id << "\t\t\t" << student.average << "\t\t\t" 
		 << grade[student.grade] << '\n' << flush;
	
	return;
}



int main ( void )
{
	DATA student[50];	// hold all student records.
	ifstream fin;	// for input
	ofstream fout;	// for output
	int i=0, numstudents, grade[5];
	float class_average;
	// grade will hold the number of grades recived in the class.
	// ex: grade[4] will hold the number of A's given to students.

	fin.open("input.txt");	// open for input
	fout.open("output.txt");	// open for output

	// lets go get the data from input.txt
	for(i=0; i<50; i++)
	{
		// the for loop will make sure we only get the first 50 lines of the file
		if(!fin.eof())	// while were not at the end of the file...
			GetStudentData(student[i], fin, grade);		// get the data for a line!
		else
			break;	// kills for loop when we reach end of file.
	}

	numstudents = i;	// holds number of students...
	// compute class average
	class_average = ( (4 * grade[4]) + (3 * grade[3]) + (2 * grade[2]) + (1 * grade[1]) ) / numstudents;

	// now we can print it all out
	// start will the ID, semester average, and letter grade for every student
	fout << "Student ID: \t Semester Average: \t Letter Grade: \n" << flush;
	for(i=0; i<=numstudents; i++)
	{
		PrintStudentData( student[i], fout);
	}

	// now print class average and grade distribution
	fout << "\n\nClass Average: " << class_average << flush;
	fout << "\n Grade Distribution: \n" 
		 << "A \t" << grade[4]
		 << "\nB\t" << grade[3]
		 << "\nC\t" << grade[2]
		 << "\nD\t" << grade[1]
		 << "\nF\t" << grade[0] << flush;

	fout << "\n\nNumber of Students: " << numstudents << flush;

	// and then we die very quietly... 
	return 0;
}

Thanks in advance for any help!

[Technocrat]

The problem you have is that DATA student[50]; is not global or static, so everytime you leave main it gets filled with junk, thus it blows up your program. Just change the dec. to static DATA student[50];

Since I dont have the txt files to check it with I dont know what other problems you might have.

[Sevengraff]

DATA is global. It does change when i leave main. I've found the problem is somewhere around numstudents = i;, because it will output to a file until that point, then die.

[Technocrat]

Hmm ok, until I made the static it would crash going to:

fout << student.id << "\t\t\t" << student.average << "\t\t\t" 
         << grade[student.grade] << '\n' << flush; 

because student.grade was always a bad number. If you give me a sample file I will look at it some more.

[Sevengraff]

sure, here is a sample input file.

... ok it didnt attach.

input.txt:
1	68	75	84
2	64	58	50
3	75	84	88
4	80	89	94
5	66	64	94
6	68	84	95

[Technocrat]

I hope I didn't just do your homework for you

Here is the code I used and it worked for me

I noted the changes with //<-------------------- (TECH)

// 
// Nicholas Funnell
// Assignment #1
// january 29, 2003
// -------------------
// Takes data from input.txt, processes test scores and sends output to output.txt
//

#include <fstream>

using namespace std;

struct DATA
{
    // holds data about student that will be printed to output.txt
    int id;
    int average;
    int grade;
};

void GetStudentData ( DATA &student, ifstream &fin, int grade[5] )
{
    // *** GetStudentData() will get one line from the file opened by fin 
    // (we will open input.txt in main() ) Takes the values from the line and
    // puts them in a struct, and also computes the students average grade and
    // letter grade.

    int letter_grade, test1, test2, testFinal;
    
    fin >> student.id >> test1 >> test2 >> testFinal; // read in from file.
    student.average = int(0.20 * test1 + 0.30 * test2 + 0.50 * testFinal);
                                            // compute average semester grade
    
    // here we decide which letter grade student got
    if(student.average >= 90)
        letter_grade = 4;    // grade: A
    else if(student.average >= 80 && student.average <= 89)
        letter_grade = 3;    // grade: B
    else if(student.average >= 70 && student.average <= 79)
        letter_grade = 2;    // grade: C
    else if(student.average >= 60 && student.average <= 69)
        letter_grade = 1;    // grade: D
    else 
        letter_grade = 0;    // grade: F
    // now assign that grade to the student & update the count of that grade 
    student.grade = letter_grade;
    grade[letter_grade] += 1;       // keeping track of number of grades
    // end of function
    return;
}

void PrintStudentData ( DATA &student, ofstream &fout )
{
    char grade[5];    // letter grades.
    grade[0] = 'F';
    grade[1] = 'D';
    grade[2] = 'C';
    grade[3] = 'B';
    grade[4] = 'A';
    // print out the stuff on a student one line at a time...
    fout << student.id << "\t\t\t" << student.average << "\t\t\t" 
         << grade[student.grade] << '\n' << flush;
    
    return;
}



int main ( void )
{
    
    static DATA student[50];    // hold all student records.   //<-------------------- Changed To Static (TECH)
    ifstream fin;    // for input
    ofstream fout;    // for output
    static int i=0, numstudents, grade[5];   //<-------------------- Changed To Static (TECH)
    float class_average;
    // grade will hold the number of grades recived in the class.
    // ex: grade[4] will hold the number of A's given to students.

    fin.open("input.txt");    // open for input
    fout.open("output.txt");    // open for output

    // lets go get the data from input.txt
    for(i=0; i<50; i++)
    {
        // the for loop will make sure we only get the first 50 lines of the file
        if(!fin.eof())    // while were not at the end of the file...
            GetStudentData(student[i], fin, grade);        // get the data for a line!
        else
            break;    // kills for loop when we reach end of file.
    }

    numstudents = i-1;    // holds number of students...  //<-------------------- When you exit your loop above you will have looped one time to many due to the check for eof.  So you need to take off one from i (TECH)
    // compute class average
    class_average = ( (4 * grade[4]) + (3 * grade[3]) + (2 * grade[2]) + (1 * grade[1]) ) / numstudents;

    // now we can print it all out
    // start will the ID, semester average, and letter grade for every student
    fout << "Student ID: \t Semester Average: \t Letter Grade: \n" << flush;
    for(i=0; i<=numstudents; i++)
    {
        PrintStudentData( student[i], fout);
    }

    // now print class average and grade distribution
    fout << "\n\nClass Average: " << class_average << flush;
    fout << "\n Grade Distribution: \n" 
         << "A \t" << grade[4]
         << "\nB\t" << grade[3]
         << "\nC\t" << grade[2]
         << "\nD\t" << grade[1]
         << "\nF\t" << grade[0] << flush;

    fout << "\n\nNumber of Students: " << numstudents << flush;

    // and then we die very quietly... 
    return 0;
} 

[Sevengraff]

wow, it works. Thanks! No, you didn't do it for me, but now i need to go look up what static does so it makes sense again.

[Technocrat]

Your welcome
I was just messing with ya, you did all the work I just helped you fix it.

[Sevengraff]

So, why did i need to make those variables static? Was I not passing them into the functions correctly? How should I have done that?

[Technocrat]

It really only matters to grade[] because you are not using a pointer to it when you leave main() and go to GetStudentData(). Since you didn't have it static, the memory was getting over writen. Try it an look the result you get.

You could have fixed this by using a pointer in GetStudentData() for student. You really didn't need to make student[]. I was just getting a currupt location when I was running it without the test file. So you can take that off