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small program stuck at segmentation fault (mean, median... using arrays)

This is a discussion on small program stuck at segmentation fault (mean, median... using arrays) within the C Programming forums, part of the General Programming Boards category; Code: #include<stdio.h>#include<math.h> double mean(int marks[], int n); double variance(int marks[], int n); double stdDev(int marks[], int n); double mode(int marks[], ...

  1. #1
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    small program stuck at segmentation fault (mean, median... using arrays)

    Code:
    #include<stdio.h>#include<math.h>
    
    
    double mean(int marks[], int n);
    double variance(int marks[], int n);
    double stdDev(int marks[], int n);
    double mode(int marks[], int n);
    void sort(int marks[], int n);
    
    
    int main(){
        
        int n;
        int t2, t3, t4;
        double t1;
        printf("test0");
    
    
    
    
        
    
    
    
    
    
    
        FILE *inFile;
    
    
        inFile=fopen("marks.txt", "r");
        if (inFile==NULL)
        {
            printf("File open error!\n");
            return 0;
        }
        printf("test1");
        
        int marks[n];
        n=0;
        printf("test2");
        while((fscanf(inFile, "%d", &marks[n]))==1) n++;
        printf("%d\n", n);
        
    
    
    
    
        t1=mean(marks, n);
        t2=variance(marks, n);
        t3=stdDev(marks, n);
        t4=mode(marks, n);
    
    
        printf("%lf %d %lf %d, mean, variance, stdDev, mode", t1, t2, t3, t4);
        fclose(inFile);
        return 0;
    }
    
    
    
    
    double mean(int marks[], int n){
        int i;
        int sum=0;
        for(i=0; i<n; i++) sum+=marks[i];
        return (1.0*sum/n);
    }
    
    
    double variance(int marks[], int n){
        int i;
        double ave, varsum;
        varsum=0;
        ave=mean(marks, n);
        for (i=0; i<n; i++) varsum+=(marks[i]-ave)*(marks[i]-ave);
        return (varsum/n);
    }
    double stdDev(int marks[], int n){
        int i;
        double var;
        var=variance(marks, n);
        return (sqrt(var));
    }
    
    
    double mode(int marks[], int n){
        int i, count=0;
        double mid;
        mid=n/2.0;
        sort(marks, n);
        for(i=0; i<n; i++){
            count=+marks[i];
            if (count==mid) return ((marks[i]+marks[i+1])/2.0); 
            if (count>mid) return(marks[i]);}
            return 0;
    
    
    
    
        } 
    
    
        void sort(int marks[], int n){
            int sorter[n];
            sorter[0]=marks[0];
            int i, temp;
            for(i=1; i<n; i++){
                if (marks[i]>=sorter[i]) sorter[i+1]=marks[i];
                else { 
                    temp=sorter[i];
                    sorter[i]=marks[i];
                    sorter[i+1]=temp;
                }
            }
    
    
                for (i=0; i<n; i++) marks[i]=sorter[i];
                return;}
    I can't find where the error occurs. The function names represent what the function does (finds mean etc.). I tried some error testing printf, but even those do not print.

  2. #2
    and the hat of wrongness Salem's Avatar
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    int marks[n];
    n=0;
    printf("test2");
    while((fscanf(inFile, "%d", &marks[n]))==1) n++;
    printf("%d\n", n);

    None of this makes any sense.
    n is uninitialised at the time you create your array - who knows what that is going to give you.

    What you DON'T have is an array that magically expands with every increment of n in that loop.

    Use two while loops
    - one to simply count how many integers would be read
    - allocate the space
    - fseek() back to the start of the file, and clearerr() to reset end of file status
    - read at most n integers from the file.
    smokeyangel likes this.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
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    Yep - exactly what Salem said. Count the numbers, then allocate the space, then read them.


    Is the compiler warning you about this line?

    Code:
    int marks[n];
    I'd expect most compilers to complain about this: something like "using uninitialised variable", or "variable may not be initalised". It's worth taking notice of compiler warnings!

  4. #4
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    Oct 2011
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    sorry, i started on learning array yesterday. my lecture notes are vague as hell . working on it starting now

  5. #5
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    Thanks to you, the segmentation error is gone, but I think I do not know the right way to pass array from one function to another:
    how to pass array from one function into another: variance to mean


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