C first and third quartiles from random sorted array

Question

I need to write code to print the first and the third quartile from a sorted and random array. I don't know how to get around it. Any help? If you need any clarifications about the code ask please. Thanks!

And if you could find a bug why the median() function won't work I'd be grateful. I think it's stuck in infinity loop.

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<math.h>
#define TABLE_SIZE 20
#define HISTOGRAM_SIZE 9

int tablica[TABLE_SIZE];
int histogram[HISTOGRAM_SIZE];


void wylosuj_tablice() //creates and randomizes the array
{
    int i;
    srand(time(0));
    for(i=0;i<TABLE_SIZE;i++)
    {
        tablica[i]=(rand()%HISTOGRAM_SIZE);
    }
}

void czysc_histogram() //cleans histogram
{
    int i;
    for(i=0; i<HISTOGRAM_SIZE; i++) {
        histogram[i] = 0;
    }
}

void tworz_histogram() //counts from 0 to 8
{
    int i;
    czysc_histogram();
    for(i=0; i<TABLE_SIZE; i++) {
        histogram[tablica[i]]++;
    }

}

void wyswietl_histogram() // shows histogram from -4 to 4
{
    int i;
    for(i=0; i<HISTOGRAM_SIZE; i++) {
        printf("Liczba %d: %d\n", i-4 /* <== */, histogram[i]);
    }
}

void wyswietl_tablice() //shows the sorted array from -4 to 4
{
    int i;
    for(i=0; i<TABLE_SIZE; i++) {
        printf ("tablica[%d]=%d\n", i, tablica[i]-4 /* <== */);
    }
}

float median() {
    int temp;
    int i, j;
    for (i=0; i<HISTOGRAM_SIZE-1; j++) {
        for(j=i+1; j<HISTOGRAM_SIZE; j++) {
            if(tablica[j] < tablica[i]) {
                //replaces elements
                temp = tablica[i];
                tablica[i] = tablica[j];
                tablica[j] = temp;
            }
        }
    }

    if (HISTOGRAM_SIZE%2==0) {
            //if there are 2 even numbers then it return mean from them
        int wynik1 = ( (tablica[HISTOGRAM_SIZE/2] + tablica[HISTOGRAM_SIZE/2 -1]) /2.0);
        printf("%d", wynik1);

    } else {
        //if there isn't then it gives the middle one
        int wynik2 =  tablica[HISTOGRAM_SIZE/2];
        printf("%d", wynik2);
    }

}

int main()
{
    wylosuj_tablice(); //executes voids
    wyswietl_tablice();
    tworz_histogram();
    wyswietl_histogram();
    median();
    return 0;
}

Answer 1

Not sure what's exactly a "quartile" here... Something like this ?

void printQuartile(int quartile)
{
    wylosuj_tablice(); // To produce the data

    int i, start, end;
    switch(quartile) {
        case 1: start = 0; end = TABLE_SIZE / 4;                  break;
        case 2: start = TABLE_SIZE / 4; end = TABLE_SIZE / 2;     break;
        case 3: start = TABLE_SIZE / 2; end = (TABLE_SIZE / 4) * 3; break;
        case 4: start = (TABLE_SIZE / 4) * 3; end = TABLE_SIZE;  break;
        default: return;
    }
    for(i= start; I<end; i++) {
        printf ("tablica[%d]=%d\n", i, tablica[i]-4);
    }
}

printQuartile(1);
printQuartile(3);

Output :

tablica[0]=-4
tablica[1]=4
tablica[2]=2
tablica[3]=-1
tablica[4]=2

tablica[10]=-1
tablica[11]=3
tablica[12]=1
tablica[13]=1
tablica[14]=4