Custom Sorting algorithm (C) [closed] - c

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Our teacher asked us today to make a custom sorting algorithm, and he gave us some instructions, however I wasn't able to solve it:
First you get the smallest number from a randomly generated array and assign it to a separate array. Then you get the second smallest number the array and assign it to the next position in the separate array.
I was able to build this, but it doesn't fully work:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define ANZAHL 5
int main() {
srand(time(0));
int zfeld[ANZAHL], zfeld1[ANZAHL] = {}, zfeld2[ANZAHL] = {}, i, d, ug, og, kl = ANZAHL + 1;
printf("Gib die untere und obere grenze an");
scanf("%d%d", &ug, &og);
for (i = 0; i < ANZAHL; i++) {
zfeld[i] = rand() % ((og - ug) - 1) + ug + 1;
}
for (d = 0; d < ANZAHL; d++) {
for (i = 0; i < ANZAHL; i++) {
if (zfeld[i] < kl && zfeld[i] != zfeld2[d - 1]) {
kl = zfeld[i];
}
}
zfeld2[d] = kl;
}
return 0;
}

Answer 1

Several issues:
kl=ANZAHL+1: the length of the original array has nothing to do with values. It would make more sense to do kl = og. But still, the place where you do this assignment is wrong. Once you have found the first minimum value, kl will be too small to detect the next smallest value: you need to reset it each time you iterate in the outer loop.
The inner loop should not iterate over all elements when you have already identified a few small values. You try to avoid to pick the same one twice, but just comparing with the previously identified value (zfeld[i] != zfeld2[d-1]) is not going to work. First, because when d is zero, this is an invalid reference, and second: there are in general more values in zfeld2 which you also don't want to select again. Instead consider that the first array should become "shorter". You can do this by moving the last value of the array into the slot where you found the smallest value. Then you can consider that the array became one unit smaller without losing any information. To make that work, you need to know the index where you find the smallest value.
So here is the corrected code for the loops:
for(d=0; d<ANZAHL; d++)
{
// Reset the index, and just consider the first value to the the smallest so far
int indexOfSmallest = 0;
// Each time you move one value, we look at one value less in this loop:
for(i=1; i<ANZAHL - d; i++)
{
if(zfeld[i] < zfeld[indexOfSmallest])
{
indexOfSmallest = i;
}
}
zfeld2[d] = zfeld[indexOfSmallest];
// Move last value in the slot that opens up:
zfeld[indexOfSmallest] = zfeld[ANZAHL - d - 1];
}
NB: this is a variant to selection sort. Selection sort does not use a second array, as it reuses the space that is liberated in the first array to store the sorted values.
I would also suggest to use better variable names. Names like kl, ug, og are maybe clear to you, but it is better practice to just use full names: kleinste, untereGrenze, ...etc.