C语言：输出杨辉三角形前n行

#include <stdio.h>
#define N 10
main()
{
    int shu[N][N]={0},a,b,c;
    for(a=0;a<N;a++)
    {
    for(c=N-1-a;c>=0;c=c-1)
    printf("  ") ;
    for(b=0;b<=a;b++)
    {
        shu[a][b]=1;
        if(!(a==0 || a==b)) shu[a][b]=shu[a-1][b-1]+shu[a-1][b];
        printf("%3d ",shu[a][b]);
    }
printf("\n");
}
 getchar();
 }