call_by_reference_shellsort.c

#include <stdio.h>
#include <malloc.h>
#define FIN "algsort.in"
#define FOUT "algsort.out"
 
int* read(int* arr, int* n) {
 
     int i, 
         num;
 
     freopen(FIN, "r", stdin);     
 
     scanf("%d",&num);
 
     arr = (int*)malloc(sizeof(int)*num);
 
      *n = num;  
 
     for(i = 0; i < num; ++i) scanf("%d", (arr+i));
 
     fclose(stdin);
 
      
return arr;
};
 
 
void write(int *arr, int num) {
 
     freopen(FOUT, "w", stdout);     
 
     int i;
 
     for(i = 0; i < num; ++i) printf("%d ", *(arr+i));
 
     free( arr );
 
     fclose( stdout );
};
 
void shellsort(int *arr, int n) {
 
     int i,
         j,
         gaps,
         gap,
         temp; 
 
     for(gaps = n/2; gaps > 0; gaps/=2) {
 
         gap = gaps;
 
         for(i = gap; i < n; ++i) {
 
             temp = arr[ i ];
 
             for(j = i - gap; ( j >= 0 && arr[j] > temp); j -= gap) {
 
                 arr[ j + gap ] = arr[ j ];
             }
 
                 arr[ j + gap ] = temp;
         } 
     }
};
 
int main() {
 
    int i,
        n, 
        *arr;  
 
    //call by reference
    arr = read( arr, &n ); 
    shellsort(arr, n);
    write( arr, n);
 
return(0);
}