Why this program to sort array doesnt work?

Question

Im trying to learn C and I'm doing this program to sort an array but It doesn't work and I'm not sure why, I tested each function and works well, someone knows if its a problem of variables or something?

#include <stdio.h>
#include <stdlib.h>

#define N 5

int V[5] = { -383, 386, 277, 415, 293 };

void displayArray(int arr[], int size)
{
    int i;
    for (i = 0; i < size; i++)
        printf("%d ", arr[i]);
}

int maxim(int v[], int n)
{
    int i, m;
    m = v[0];
    /*
    Find maxim element
    */
    for (i = 1; i < n; i++)
        if (v[i] > m)
            m = v[i];
    /*
    Search element position
    */
    for (i = 0; i < N; i++)
        if (v[i] == m)
            return i;
}

void sort(int v[], int n)
{
    int i, pos, t;
    for (i = 0; i < n; i++)
        pos = maxim(v, n - i);

        /*
        Swap elements
        */
        t = v[n - 1 - i];
        v[n - 1 - i] = v[pos];
        v[pos] = t;
}

int main()
{
    displayArray(V, N);
    sort(V, N);
    printf("\n");
    displayArray(V, N);
    return 0;
}

The output is

-383 386 277 415 293 - Original Array

21900 386 277 415 293 - 'Sorted' Array

you can accept one of the answers by clicking on the grey checkmark below its score. — chqrlie
– chqrlie, Commented Feb 14, 2022 at 19:45

WhozCraig · Accepted Answer · 2022-02-13 12:10:11Z

3

First fix your maxim function. Its purpose is to find the maximum index of a sequence v of magnitude n. Therefore, remembering the maximum value in m is irrelevant; you want to remember where it resides :

int maxim(int v[], int n)
{
    int m=0;
    for (int i=1; i<n; ++i)
    {
        if (v[m] < v[i])
            m = i; // save new max location
    }
    return m;
}

After that, the sort, which is completely wrong. This:

int i, pos, t;
for (i = 0; i < n; i++)
    pos = maxim(v, n - i);

is pointless. It calculates, and overwrites, pos repeatedly until the last iteration, which is the only one that is processed with:

t = v[n - 1 - i];
v[n - 1 - i] = v[pos];
v[pos] = t;

E..g, you sort one element, and then exit your sort. You need to sort them all, starting with the full segment, then reducing the size of the segment by one with each iteration after you swap the most-maximum element into position for that segment.

void sort(int v[], int n)
{
    for (int i=0; i<(n-1); ++i)
    {
        int m = maxim(v, (n-i)); // max of this segment
        int tmp = v[m];
        v[m] = v[n-i-1];
        v[n-i-1] = tmp;
    }
}

answered Feb 13, 2022 at 12:10

WhozCraig

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1 Comment

carlosgrt Over a year ago

It was my mistake (sort function) while putting the code in the post... I didnt check the indentation It was supossed to be inside the for loop. Anyways I tried to put curly brackets in the for loop (sort function) and It worked just doing that change...

Luis Colorado · Accepted Answer · 2022-02-14 14:31:45Z

0

Your program is inefficient, but almost correct. The only place where you must focus is:

void sort(int v[], int n)
{
    int i, pos, t;
    for (i = 0; i < n; i++)
        pos = maxim(v, n - i);

        /*
        Swap elements
        */
        t = v[n - 1 - i];
        v[n - 1 - i] = v[pos];
        v[pos] = t;
}

Well, C is not Python, so if, after getting pos you want to swap the elements of your array, then you need to group all of the for loop in braces, as in:

void sort(int v[], int n)
{
    int i, pos, t;
    for (i = 0; i < n; i++) {
        pos = maxim(v, n - i);

        /*
        Swap elements
        */
        t = v[n - 1 - i];
        v[n - 1 - i] = v[pos];
        v[pos] = t;
    }
}

answered Feb 14, 2022 at 14:31

Luis Colorado

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Comments

Gautier Blandin · Accepted Answer · 2022-02-13 12:14:07Z

0

pos = maxim(v, n - i);

should be

pos = maxim(v, n);

answered Feb 13, 2022 at 12:14

Gautier Blandin

362 bronze badges

1 Comment

carlosgrt Over a year ago

the purpose if n-i is to limit the range of finding the max element because the array gets sorted every iteration by 1 element starting from the end of the array. Its solved anyways thanks for answer

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