Problem in merge sort..array sort

[Awais Tahir]

HI there i am doing merge sort technique to sort Array..
But i got no error But the OUT console shows nothing. ithink problem is at LINE 21...
Plz suggest me to control this problem.

#include<iostream.h>
#include<conio.h>
#include<process.h>
void msort(int arr[],int start,int end);
void merge(int arr[],int start,int half,int end);

void main()
 {
   clrscr();
    int arr[20]={22,33,11,10,9,8,7,77,45};
    int end=9;
    int start=1;
    msort(arr,start,end);
    for(int i=1;i<=9;i++)
    cout<<arr[i]<<"/n";
    getch();
 }
void msort(int arr[],int start,int end)
{ int  half;
  if(start==end)
  return;              // what will it should returned when start and 
                            // end have become ??????????
  half=(start+end)/2;
  msort(arr,start,half);
  msort(arr,half+1,end);
  merge(arr,start,half,end);

}
void merge(int arr[],int start,int half,int end)
{int n1,n2,j,k;
int left[20],right[20];
 n1=half-start+1; n2=end-half;
 for(int i=1;i<=n1;i++)
	left[i]=arr[start+i-1];
 for(i=1;i<=n2;i++)
	right[i]=arr[half+i];
 i=j=1; k=start;
 while(i<=n1&&j<=n2)
{
	 if(left[i]<=right[i])
	{
	  arr[k]=left[i];
	  i++;
	}
	  else

	  {
	  arr[k]=right[j];
	  j++;

	  }
    k++;
 }

 if(i<=n1)
	{
	while(i<=n1)
       {	arr[k]=left[i];
	i++;
	j++;}
	}
 else
	{
	 while(j<=n2)
	 arr[k]=right[j];
	 j++;
	 k++;


    }
}

[Peter87]

I don't understand how this code can even compile. Where is i on line 35 and below defined?

[Awais Tahir]

look at line 33 in for loop i is defined and initialized as well

[3qX21hU5]

For loops are in a different scope so just because i was defined and initialized in a previous for loop does not mean it will still be defined after it. Once you finish the for loop the variable disappears because it is a temporary variable.

[Peter87]

That i will only be in scope on line 33 and 34.

[Awais Tahir]

new see i have declared outside of for loop..
i think this is a local variable at it has scope within merge()

#include<iostream.h>
#include<conio.h>
#include<process.h>
void msort(int arr[],int start,int end);
void merge(int arr[],int start,int half,int end);

void main()
 {
   clrscr();
    int arr[20]={22,33,11,10,9,8,7,77,45};
    int end=9;
    int start=1;
    msort(arr,start,end);
    for(int i=1;i<=9;i++)
    cout<<arr[i]<<"/n";
    getch();
 }
void msort(int arr[],int start,int end)
{ int  half;
  if(start==end)
  return;             
  half=(start+end)/2;
  msort(arr,start,half);
  msort(arr,half+1,end);
  merge(arr,start,half,end);

}
void merge(int arr[],int start,int half,int end)
{int n1,n2,j,k, i;
int left[20],right[20];
 n1=half-start+1; n2=end-half;
 for(i=1;i<=n1;i++)      // now  i have declaer outside of for ..
	left[i]=arr[start+i-1];
 for(i=1;i<=n2;i++)
	right[i]=arr[half+i];
 i=j=1; k=start;
 while(i<=n1&&j<=n2)
{
	 if(left[i]<=right[i])
	{
	  arr[k]=left[i];
	  i++;
	}
	  else

	  {
	  arr[k]=right[j];
	  j++;

	  }
    k++;
 }

 if(i<=n1)
	{
	while(i<=n1)
       {	arr[k]=left[i];
	i++;
	j++;}
	}
 else
	{
	 while(j<=n2)
	 arr[k]=right[j];
	 j++;
	 k++;


    }
}

[Peter87]

It's getting stuck in the loop on line 63.

[Awais Tahir]

i am not getting how it can stuck here on line no 63.
here on last while loop ..the iterative variable is j
and moreover here i has no connection

[fg109]

You didn't put in brackets so only

arr[k]=right[j];

is part of the loop. The other statements are outside of the loop, which means that j and k never change.