为什么我已经存过一次账号密码了，然后第二次运行还是提示没账号
#include <stdio.h>

int main (){
    char zhanghao[16] , mima[16] , ch;    //账号        //密码
    FILE * mimawenjian;
   
    mimawenjian = fopen ("mimaben.txt","w+");
    ch = fgetc(mimawenjian);
    if (ch == EOF){
        printf ("你还没有账号，请注册一个\n账号：");
        scanf("%s",zhanghao);
        printf ("密码：");
        scanf("%s",mima);
        fprintf (mimawenjian,"%s\t\t%s",zhanghao,mima);
        fclose (mimawenjian);
        fflush(stdin);
        system("cls");
        printf("注册成功，输入任意键进入登入页面。。。。");
        getchar();
        system("cls");
    }
   
}