为什么我写的代码无法把输出写进文件out.txt里面；
下面是我的代码：
#include <stdio.h>
#include <stdlib.h>

int main()
{
    FILE *out;
    int flag=0;
    int N_;
    int i,j;
      scanf("%d",&N_);

      if((out=fopen("out.txt","w"))==NULL)
      {
          printf("Wrong!");
          return (-1);
      }
    while(N_!=0)
    {
        if(N_%2==0)
        {
            for(i=1; i<=N_; i++)
            {
                if(flag==1&&N_!=0)
                 {fputc('\n',out); printf("\n");}
                int k=1;
                for (j=0; j<2*N_-1&&k<=2*N_-1; j++)
                {
                    if (k<=N_-i)
                    {
                       fputc('\0',out); printf(" ");
                        k++;
                    }
                    else if (k>(N_-i)&&k<=(2*N_-1)-(N_-i))
                    {
                       fputc('+',out);printf("+");
                        k++;
                    }
                    else if(k>(2*N_-1)-(N_-i)&&k<=2*N_-1)
                        {
                            fputc(' ',out);printf(" ");
                        k++;}
                   flag=1;
                }
            }
        }
        else if(N_%2!=0)
        {
           for (i=N_;i>=1;i--)
            {
                if (flag==1&&N_!=0)
                {fputc('\n',out);printf("\n");}
                int k=1;
                for(j=0;j<2*N_-1&&k<=2*N_-1;j++)
                {
                    if(k<=N_-i)
                    {fputc(' ',out);printf(" ");
                    k++;}
                    else if(k>(N_-i)&&k<=(2*N_-1)-(N_-i))
                    {fputc('+',out);printf("+");
                    k++;}
                    else if(k>(2*N_-1)-(N_-i)&&k<=2*N_-1)
                    {fputc(' ',out);printf(" ");
                    k++;}
                    flag=1;
                }
            }
        }
         fputc('\n',out);printf("\n");
        scanf("%d",&N_);
    }
    fclose(out);
    return 0;
}