assigning values in file to an array

This is a discussion on assigning values in file to an array within the C++ Programming forums, part of the General Programming Boards category; Hi there, I'm doing something quite complicated and as a beginner it's baffling me. I need to create a bar ...

  1. #1
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    Unhappy 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

  2. #2
    mustang benny bennyandthejets's Avatar
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    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.
    benforbes@optusnet.com.au
    Microsoft Visual Studio .NET 2003 Enterprise Architect
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  3. #3
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    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

  4. #4
    mustang benny bennyandthejets's Avatar
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    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
    benforbes@optusnet.com.au
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  5. #5
    End Of Line Hammer's Avatar
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    >>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.
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  6. #6
    mustang benny bennyandthejets's Avatar
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    It's the same in assembler though isn't it Hammer? I admit, it looks a lot better.
    benforbes@optusnet.com.au
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  7. #7
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    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");
    }

  8. #8
    mustang benny bennyandthejets's Avatar
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    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.
    benforbes@optusnet.com.au
    Microsoft Visual Studio .NET 2003 Enterprise Architect
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  9. #9
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    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

  10. #10
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    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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