post  messed up sort

archer86 (15)   Link to this post
Can anyone shed some light as to why this small sort program doesn't work properly?

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
 
#include<iostream>
using namespace std;

double swap (int[ ], int, int); 

main(){
    	int slot[10]={8,3,1,5,7,10,4,9,6,2};
    	int n=10,i;
    	int lower, upper, sortflag, sml, scan;
    	lower=0; 
    	upper=n-1;
    	sortflag=1;
    	while((lower<upper)&&(sortflag==1)){
        	sml=lower;
        	sortflag=0;
        	scan=lower+1;
		while(scan<=upper-lower){
			if(slot[scan]>slot[scan+1]){
                 			swap(slot,scan,scan+1);
                              	sortflag=1;
				if(slot[scan]<slot[sml]) sml=scan;                         
				}//IF
			scan++;
			}//WHILE
        swap(slot,lower,sml);
	  upper=upper-1;
	  lower=lower+1;
    	}//WHILE
    	cout<<"AFTER SORT:"<<endl;
    	for(i=0;i<n;i++) cout<<slot[i]<<" ";	
    	cout<<endl;
    	return 0;       }//MAIN 

double swap(int slot[], int i,int j){
    	int temp;
      temp=slot[i];
      slot[i]=slot[j];
      slot[j]=temp;
      return 0;     }//SWAP


The output is:

AFTER SORT:
0 1 3 4 5 6 7 2 9 8

Thanks in advance.

C:\Dev-Cpp>
CamelCase (10)   Link to this post
I just ran it on my system compiled with code::blocks, it ran fine output is 1 2 3 4 5 6 7 8 9 10...
dgirdhar (6)   Link to this post
I also tried, it is working fine on my machine too.
Grey Wolf (1407)   Link to this post
Just looking over the code, Line 17, while(scan<=upper-lower){ would allow scan to go to a value of 9, you then look at slot[scan+1], which is out of bounds for slot and would result in unpredicable behavour.

Try this:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
 
#include<iostream>
using namespace std;

double swap (int[ ], int, int); 

int main()
{
    int slot[10]={8,3,1,5,7,10,4,9,6,2};
    int n=10;
    int i = 0;
    int lower = 0;
    int upper = n-1; 
    int sortflag = 1;  
    	 
    while((lower < upper) && ( sortflag==1))
    {
        sortflag = 0;

        int sml = lower;
        int scan = lower;

        while(scan < upper )
        {
            if(slot[scan] > slot[scan+1])
            {
                sortflag = 1;

                swap(slot,scan,scan+1);

                if(slot[scan]<slot[sml]) 
                    sml=scan;                         
            }
            ++scan;
        }
        swap(slot,lower,sml);
        --upper;
        ++lower;
    }
    
    cout<<"AFTER SORT:"<<endl;
    for(i=0; i<n; i++) 
        cout<<slot[i]<<" ";	
    cout<<endl;
    
    return 0;       
} 

double swap(int slot[], int i, int j)
{
    int temp;
    
    temp = slot[i];
    slot[i] = slot[j];
    slot[j] = temp;
    
    return 0;    
}
Last edited on

This topic is archived - New replies not allowed.