j=2 or j=1? of insertion sort with sentinel?

j=2.  You can also run with j=1.  The logic is exactly the same as a simple straight insertion sort.  In that case though you will run an extra loop.  The improved version can be found in Listing 1. 

Listing 1:

#include <stdio.h>
#include <limits.h>
#define N 11
int main(int c,char *v[])
{
  int A[N]={-INT_MAX,1,5,6,9,1,3,0,-2,-10,7};
  int i,j,k;
  for(j=2;j<N;j++){
    k=A[j];
    i=j-1;
    while(A[i]>k)
      A[i+1]=A[i--];
    A[i+1]=k;
  }
  for(i=1;i<N;i++)
    printf("%d ",A[i]);
  printf("\n");
  return 0;
}