Quicksort skipping one element - c

Question

So today i tried to implement a quicksort. It's almost working but somehow skips one element.
example : 5 2 8 2 3 4 1 5 7 -5 -1 -9 2 4 5 7 6 1 4
output : -5 -1 -9 1 2 2 3 2 1 4 4 4 5 5 5 6 7 7 8
In this case it skips -9. Here is code of the function.
test = quicksort_asc(0,size,tab,size) // this is function call
int quicksort_asc(int l, int r, int tab[], int tabSize) //l is first index, r is last index, tabSize is tabsize-1 generally
{
int i,buffer,lim,pivot,flag=0;
if(l == r)
return 0;
lim = l-1;
pivot = tab[r-1];
printf("pivot:%d\n",pivot);
for (i = l; i <= r-1; ++i)
{
if(tab[i] < pivot) {
lim++;
buffer = tab[lim];
tab[lim] = tab[i];
tab[i] = buffer;
flag = 1;
}
}
if(flag == 0)
return 0;
buffer = tab[lim+1];
tab[lim+1] = pivot;
tab[r-1] = buffer;
quicksort_asc(l,lim+1,tab,lim+1);//left side
quicksort_asc(lim+1,tabSize,tab,tabSize);//right side
}
This is my array length count code. 100 is maximum size, 0 is a stop value.
Count is size.
int count=0;
for (int i = 0; i < 100; i++)
{
test = scanf("%d",&vec[i]);
if(vec[i] == 0) break;
count++;
}
return count;

Answer 1

It seems nobody hurries to help you.:)
For starters the last parameter is redundant.
int quicksort_asc(int l, int r, int tab[], int tabSize);
^^^^^^^^^^^
All you need is the pointer to the first element of the array and starting and ending indices.
Also instead of the type int for the indices it is better to use the type size_t. However as you are using the expression statement
lim = l-1;
then o'k let the indices will have the type int though you could use another approach without this expression statement.
So the function should be declared like
void quicksort_asc( int tab[], int l, int r );
The variable flag is redundant. When it is equal to 0 it means that all elements before the pivot value are greater than or equal to it. But nevertheless you have to swap the pivot value with the first element that is greater than or equal to the pivot.
This loop
for (i = l; i <= r-1; ++i)
has one iteration redundant. It should be set like
for (i = l; i < r-1; ++i)
This call
quicksort_asc(lim+1,tabSize,tab,tabSize);
^^^^^ ^^^^^^^
shall be substituted for this call
quicksort_asc( lim + 2, r, tab );
^^^^^^^ ^^
because the pivot value is not included in this sub-array.
Here is a demonstrative program.
#include <stdio.h>
void quicksort_asc( int tab[], int l, int r )
{
if ( l + 1 < r )
{
int lim = l - 1;
int pivot = tab[r - 1];
for ( int i = l; i < r - 1; ++i )
{
if ( tab[i] < pivot )
{
lim++;
int tmp = tab[lim];
tab[lim] = tab[i];
tab[i] = tmp;
}
}
tab[r - 1] = tab[lim + 1];
tab[lim + 1] = pivot;
quicksort_asc( tab, l, lim + 1 );
quicksort_asc( tab, lim + 2, r );
}
}
int main(void)
{
int a[] = { 5, 2, 8, 2, 3, 4, 1, 5, 7, -5, -1, -9, 2, 4, 5, 7, 6, 1, 4 };
const int N = ( int )( sizeof( a ) / sizeof( *a ) );
for ( int i = 0; i < N; i++ )
{
printf( "%d ", a[i] );
}
putchar( '\n' );
quicksort_asc( a, 0, N );
for ( int i = 0; i < N; i++ )
{
printf( "%d ", a[i] );
}
putchar( '\n' );
return 0;
}
Its output is
5 2 8 2 3 4 1 5 7 -5 -1 -9 2 4 5 7 6 1 4
-9 -5 -1 1 1 2 2 2 3 4 4 4 5 5 5 6 7 7 8