程序代码：

#include<stdio.h>
#include<stdlib.h>
int main()
{
    FILE *fp,*fp1;
    int a,i;
    if((fp=fopen("d:\\w5.dat","wb+"))==NULL)         //文件w5.dat
    {
        printf("Cannot open!\n");
        exit(1);
    }
        for(i=0;i<20;i++)
            fprintf(fp,"%5d",2*i+1);
   
/*    for(i=0;i<20;i++)
    fp=fopen("d:\\w5.dat","rb");
    fread(a,4,20,fp);
    fclose(fp);
    if((fp=fopen("d:\\w6.dat","wb"))==NULL)
    {
        printf("Cannot open!\n");
        exit(1);
    }
    fwrite(a,4,20,fp);
    fclose(fp);
    */  //此方法不可行
    if((fp1=fopen("d:\\w6.dat","wb"))==NULL)         //文件w6.dat
    {
        printf("Cannot open!\n");
        exit(1);
    }
    for(i=0;i<20;i++)
    {
        fscanf(fp,"%d",&a);
        printf("%15d",a);
        fprintf(fp1,"%5d",a);
    }
    fclose(fp);
    fclose(fp1);
    return 0;
}