Algorithm for the implementation of merge sort using link array(pointers)

Question

 int a[SIZE];
 int link[SIZE];              
 
 int MergeLists(int i, int j)
 {
 int head;
 int *pprev = &head;                  
     while((i != -1) && (j != -1)){      
         if(a[i] <= a[j]){               
             *pprev = i;                 
             pprev = &link[i];           
             i=*pprev;                   
         } else {                        
             *pprev = j;                 
             pprev = &link[j];           
             j=*pprev;                   
         }
     }
     if(i == -1)                         
         *pprev=j;                       
     else                                
         *pprev=i;
 
     printf("%d head",head);                    
     return head;
 }
 
 int MergeSort(int low, int end)
 {
 int mid, i, j;
     if((end - low) == 0){               
         return low;                     
     }
     if((end - low) == 1){               
         link[low] = -1;                 
         return low;                     
     }
     if((end - low) == 2){               
         if(a[low] <= a[end-1]){         
             link[low]   = end-1;        
             link[end-1] = -1;
             return low;                 
         } else {                       
             link[end-1] = low;          
             link[low]   = -1;
             return end-1;               
         }
     }
     mid = (low+end)/2;                  
     i = MergeSort(low, mid);            
     j = MergeSort(mid, end);           
     return MergeLists(i, j);            
 }
 
 int main()
 {
 int i;
 for(i=0;i<SIZE;++i)
     {
         printf("\nenter element number %d: ",i+1);
         scanf("%d",&a[i]);
     }
     i = MergeSort(1, SIZE);
     do{
         printf("%3d", a[i]);
         i = link[i];
     }while(i != -1);
     return 0;
 }

to implement merge sort using link array(pinters) error is given below input 4 5 2 1 output 1 2 5 MergeLists() uses head for the start of a list (the old code uses link[0]), and -1 for the end of a list (the old code uses 0). This allows sorting of a[0] to a[n-1] (the old code was sorting a[1] to a[n], with a[0] unused).

Answer 1

Well, it seems to be a minor problem, just change the function call in main to

i = MergeSort(0, SIZE);

In C or C++, the index starts with 0, and it is also true when we try to write a function.