Four Sorting Algorithms in C

#include <stdio.h>
#include <stdlib.h>
typedef int Item;
#define key(A) (A)
#define less(A, B) (key(A) < key(B))
#define exch(A, B) { Item t = A; A = B; B = t; } 
#define compexch(A, B) if (less(B, A)) exch(A, B)
void sort(Item a[], int l, int r)
  { int i, j; 
    for (i = l+1; i <= r; i++)
      for (j = i; j > l; j--) 
        compexch(a[j-1], a[j]);
  }
main(int argc, char *argv[])
  { int i, N = atoi(argv[1]), sw = atoi(argv[2]);
    int *a = malloc(N*sizeof(int));
    if (sw) 
      for (i = 0; i < N; i++) 
        a[i] = 1000*(1.0*rand()/RAND_MAX);
    else 
      while (scanf("%d", &a[N]) == 1) N++; 
    sort(a, 0, N-1);
    for (i = 0; i < N; i++) printf("%3d ", a[i]);
    printf("\n");
  }
-----
void selection(Item a[], int l, int r)
  { int i, j;
    for (i = l; i < r; i++)
      { int min = i;
        for (j = i+1; j <= r; j++) 
            if (less(a[j], a[min])) min = j;
        exch(a[i], a[min]);
      } 
  }
-----
void insertion(Item a[], int l, int r)
  { int i;
    for (i = l+1; i <= r; i++) compexch(a[l], a[i]);
    for (i = l+2; i <= r; i++)
      { int j = i; Item v = a[i]; 
        while (less(v, a[j-1]))
          { a[j] = a[j-1]; j--; }
        a[j] = v; 
      } 
  }
-----
void bubble(Item a[], int l, int r)
  { int i, j;
    for (i = l; i < r; i++)
      for (j = r; j > i; j--)
        compexch(a[j-1], a[j]);
  }
-----
void shellsort(Item a[], int l, int r)
  { int i, j, h; 
    for (h = 1; h <= (r-l)/9; h = 3*h+1) ;
    for ( ; h > 0; h /= 3)
      for (i = l+h; i <= r; i++)
        { int j = i; Item v = a[i]; 
          while (j >= l+h && less(v, a[j-h]))
            { a[j] = a[j-h]; j -= h; }
          a[j] = v; 
        } 
  }