求助，运行错误，求解

[敲风奏雨]

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define SIZE 20
int i=0;
FILE*fp;
struct account
{int id;
char name[10];
float balance;
}newone[SIZE];

int main(){
printf("请输入账号:");
scanf("%d",&newone[i].id);
printf("账户名:");
scanf("%s",&newone[i].name);
printf("账户余额:");
newone[i].balance=0.0;
scanf("%f",&newone[i].balance);

if(fopen("date.dat","wb")==NULL){
printf("cannot open file\n");
exit(0);
}
if(fwrite(&newone[i],sizeof(struct account)+1,1,fp)!=1)printf("write file orror\n");
fclose(fp);
i++;
}

[幻夢之葉]

if(fopen("date.dat","wb")==NULL) 修改为 if ((fp = fopen("date.dat", "wb")) == NULL) 你fp没有赋值就使用了（NULL）