Creating a histogram in C

Question

I have tried many different approaches and it keeps giving me errors...I am definitely not the best coder, please help! I have tried to create a histogram in many different ways, I know the logic behind making a histogram but I do not know how to implement that into C. I need to create a histogram for the x array.

The problem: Write a computer routine to generate 2,000 values from the given cdf F(x)=x^4/16 on 0<=x<=2. Make a histogram of the 2,000 values and compare it to the theoretical cdf.

int main()
{
    int i, b, d, e, j, bins=9, n=2000, y[2000], hist[9];
    double seed = 12;
    double temp=0, r[2000], temp2=0, x[2000];
    int a = 1093, c = 18257, m = 86436;
    
    printf("\nThis program will calculate random variates based on the given CDF\n :x^4/16 on 0<=x<=2\n ");


y[0]=seed;
    for (i=1; i<n; i=i+1){
        y[i] = (a*y[i-1] + c) % m;
        temp = y[i];
        r[i] = temp / m;
        temp2 = r[i];
        x[i] = pow(16*temp2,0.25);
        printf("%d %.4lf %lf\n", y[i], r[i], x[i]);
        
    }

//all of my attempts below
/*
        int *buildHist(int bins, double min, double max, int n, double *data){
   double *hist=malloc(bins*sizeof(int));
   if (hist == NULL) return hist;
   for (int i=0; i<n; ++i){
      int bin=int( (data[i]-min)/((max-min)/(bins)) );
      if ( (bin>=0) && (bin<n) ) hist[bin]++;
   }
   return hist;
}


    int max = x[0];
    for (d = 1; d < n; d=d+1){
        if (x[d] > max)
        max = x[d];
        
    }
    printf("The max is : %lf\n", max);
    
    int min = x[0];
    for (b =1; b<n; b=b+1){
        if (x[b] < min)
        min = x[b];
        
    }
    printf("The min is : %lf\n", min);
    
    
    //Dividing data into bins
for (b = 0; b < n; b+1){
    for (j = 1; j <= bins; j+1){

        float bin_max = (float)j / (float)bins;
        if (x[b] <= bin_max){
            hist[j]+1;
            break;
        }
    }
}
// Plotting histogram
printf("\n\nHistogram of Float data\n");
for (d = 1; d <= bins; d+1){
    count = hist[d];
    printf("0.%d |", d - 1);
    for (e = 0; e < count; e+1)
    {
        printf("%c", (char)254u);
    }
    printf("\n");
}
    */

return 0;
}

Answer 1

I guess that your problem is that malloc() returns non-initialized memory. This means that your hist already contains garbage values which you then increment with hist[bin]++ .

Use calloc() to allocate hist or use the memset() C library function to clear hist before use.