2．题目：编一个Ｃ程序，它能读入文件ｆ１．ｃ和ｆ２．ｃ中的所有整数，并把这些数按从小到大的次序写到文件ｆ３．ｃ中，文件中的相邻两个整数都用空格或换行符隔开。(注：可执行文件名为e9_2.exe)

程序设计：
#include "stdio.h"
main()
{FILE *fp1,*fp2,*fp3;
int a[100],n,i,j,k,x;
if ((fp1=fopen("f1.c","wb"))==NULL)
{printf("f1.c can not open!\n");
exit(0);
}
x=9999;
while (x!=-9999)
{scanf("%d",&x);
if (x!=-9999) fwrite(&x,sizeof(int),1,fp1);
}
fclose(fp1);
if ((fp2=fopen("f2.c","wb"))==NULL)
{printf("f2.c can not open!\n");
exit(0);
}
x=9999;
while (x!=-9999)
{scanf("%d",&x);
if (x!=-9999) fwrite(&x,sizeof(int),1,fp2);
}
fclose(fp2);
if ((fp1=fopen("f1.c","rb"))==NULL)
{printf("f1.c can not open!\n");
exit(0);
}
if ((fp2=fopen("f2.c","rb"))==NULL)
{printf("f2.c can not open!\n");
exit(0);
}
if ((fp3=fopen("f3.c","wb"))==NULL)
{printf("f3.c can not open!\n");
exit(0);
}
i=-1;
while (!feof(fp1))
fread(&a[++i],sizeof(int),1,fp1);
fclose(fp1);
i--;
rewind(fp2);
while (!feof(fp2))
fread(&a[++i],sizeof(int),1,fp2);
fclose(fp2);
n=i;
for (k=1;k<n;k++)
for (j=n-1,i=0;i<n-k;i++,j--)
if (a[j]<a[j-1])
{x=a[j];a[j]=a[j-1];a[j-1]=x;}
fwrite(a,sizeof(int),n,fp3);
fclose(fp3);
if ((fp3=fopen("f3.c","rb"))==NULL)
{printf("f3.c can not open!\n");
exit(0);
}
while (!feof(fp3))
{fread(&x,sizeof(int),1,fp3);
printf("%d ",x);
}
printf("\n");
}