assigning values in file to an array

**divinyl** · 07-29-2003

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

**bennyandthejets** · 07-29-2003

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.

**divinyl** · 07-29-2003

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

**bennyandthejets** · 07-29-2003

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

**Hammer** · 07-29-2003

>>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.

**bennyandthejets** · 07-29-2003

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

**laasunde** · 07-29-2003

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");
}

**bennyandthejets** · 07-29-2003

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.

**laasunde** · 07-29-2003

I see your point but the original post ask for

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

**laasunde** · 07-29-2003

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.

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