C语言程序设计修改。

把变量double x=3.12;的值以追加方式用fwritw()函数储存在文件中，然后用fread()读取后赋值给变量y。

#include"stdio.h"
void main()
{   int i;
    int p1[10]= {23,45,12,-56,78,34,30,-19,50,
                 -100
                };
    int p2[10];
    FILE* df;
    df=fopen("d:\\tc30\\usr\\bakup.dat","wb+");
    fwrite(p1,4,10,df);
    rewind(df);
    fread(p2,4,10,df);
    fclose(df);
    for(i=0; i<10; i++)
        printf("%d\n",p2[i]);
}

追加用a模式

#include "stdio.h"

int main()
{
    int i;
    int p1[10] = {23, 45, 12, -56, 78, 34, 30, -19, 50,
                  -100};
    int p2[10];
    FILE *df;
    
    df = fopen("bakup.dat", "w");
    fwrite(p1, sizeof(p1[0]), 10, df);
    fclose(df);

    double x = 3.12, x2;
    df = fopen("bakup.dat", "a+");
    fwrite(&x, sizeof(x), 1, df);
    rewind(df);

    fread(p2, sizeof(p2[0]), 10, df);
    fread(&x2, sizeof(x), 1, df);
    fclose(df);

    for (i = 0; i < 10; i++)
        printf("%d\n", p2[i]);
    printf("%lf\n", x2);

    return 0;
}