assigning values in file to an array

Hi there,

I'm doing something quite complicated and as a beginner it's baffling me. I need to create a bar chart based on values read in from a file. For example, say the file contains grades of university students between 0 and 100%. I need to store the results in an array, as well as their frequency (as in, how many times a specific grade has been scored). My idea was a two dimensional array- grades and their frequency. But can anyone help me out with some syntax? How to assign contents from a file to a two dimensional array, and how would i declare the array without knowing it's initial values?

ANy help much appreciated.

Thanks
Divinyl

What is the format of the file? If there is a definitive, regular format, it shouldn't be too hard. You could just call fgetc() and retrieve characters one at a time, until you hit a bracket. Then start storing characters in a string, and stop when you hit another bracket. Convert the string to a number using atoi().

One tip, instead of using two dimensional arrays, you could use structs. They're more descriptive of the array. Ie:

Code:

---

struct gradeStruct
{
int grade;
int freq;
}

gradeStruct grades[50];

grades[0].grade=GetGradeFromFile();
grades[0].freq=GetFreqFromFile();

---

All you have to do is makes those two functions, and a suitable loop.

So, post the format of the file, and I'll have a look.

Thank you for replying. Yes, the struct is more clear than an array.

The file just contains a long list of 100 different numbers, from 0 - 100. I.e. the grades of 100 students. Like this:

22
67
89
40

and so on...

But there is no reference to frequencies, so i guess i have to do some sort of count...each time a number occurs, add the to an int variable. Any ideas on where i might put this count and the syntax?

Thanks again

One of the easiest ways may be to convert the grade input (string) to an integer, and use that as an offset in the array. Ie:

Code:

---

int grades[100];
char *temp;
int nOffset;

memset((LPVOID)&grades,0,100*sizeof(int));

for (int i=0;i<100;i++)
{
temp=GetGrade();
nOffset=atoi(temp)-1;
grades[nOffset]++;
}

---

Or something like that.

EDIT: Coding errors

>>memset((LPVOID)&grades,0,100*sizeof(int));
Yak! This is better:
>>int grades[100] = {0};

If you're doing this:
>>grades[nOffset]++;
make sure that nOffset is within the array bounds first.

It's the same in assembler though isn't it Hammer? I admit, it looks a lot better.

something like this should work...

Code:

---

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
    string temp;
    int grades[100]={0};
    int counter=0;
    ifstream file("c:/temp/temp.txt");
   
    while(!file.eof() )
    {
        getline(file, temp);
        grades[counter++] = atoi( temp.c_str() );
    }
    file.close();
   
    for (int index=0; index < counter; index++)
        cout << grades[index] << '\t';
    cout << endl << endl;
   
    int freq[100] = {0};
    for (int x=0; x < 100; x++)
    {
        int temp = grades[x];
        if (temp > 0)
                freq[temp] += 1;
    }
   
    for(int y=0; y < 100; y++)
        if (freq[y] > 0)
                cout << "There were " << freq[y] << " students who got " << y << '%' << endl;
               
    system("PAUSE");
}

---

You can halve the memory required by incrementing the count directly into the grades array. Change your code to this:

Code:

---

while(!file.eof() )
    {
        getline(file, temp);
        grades[atoi( temp.c_str() )]++;
    }

---

Maybe a bit of code to check validity of input, nothing too complex. Doing it my way, you reduce the code a lot.

Another tip, you declare temp twice, once as a string, once as an int. You should change the name.

I see your point but the original post ask for

Quote:

---

I need to store the results in an array, as well as their frequency.

---

your way only stores the frequency.

I fully agree that my code is far from complete, it's just a quick and simple example to give the guy an idea of how to do it :)

Maybe this code is a bit better...

Code:

---

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
    string temp;
    int grades[100]={0};
    int freq[100] = {0};
    int counter=0;
    ifstream file("c:/temp/temp.txt");
   
    while(!file.eof() )
    {
        getline(file, temp);
        grades[counter++] = atoi( temp.c_str() );
        freq[atoi( temp.c_str() )]++;

    }

    for (int index=0; index < counter; index++)
        cout << grades[index] << '\t';
    cout << endl << endl;
   
    for(int y=0; y < 100; y++)
        if (freq[y] > 0)
                cout << "There were " << freq[y] << " students who got " << y << '%' << endl;
   
    file.close();   
    system("PAUSE");
}

---

I'll leave check validity of input up to others.