谢谢dat文件为什么建不出来，查询数据是乱码。

小白在线等

又是一个贴图党

等下我把源代码发过来，能帮我看一下嘛？

#define  _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<conio.h>
#define Max 8
char key[Max];
int step = 0;
char passwords_1[Max];
typedef struct da
{
    int day;
    float price1;
    float price2;
    float price3;
    struct da *next;
}data;
int login();//登陆模块
void make_note();//记录模块
void found();//查询模块
void choice();//菜单界面
void ending();//结束模块


void main()
{
    for(step=1;step<Max;step++ )
    {
    key[step] = 1;
    }
    login( );
   
}


void choice ()
{
    char choose;
    while(1)
    {
        fflush(stdin);
        printf("请选择要执行的操作:\n");
        printf("A.记录账本\n");
        printf("B.查询旧账目\n");
        printf("C.结束程序\n");
        printf("请输入您的选项：");
        choose=getchar();
        system("pause");
        system("cls");
        switch (choose)
        {
            case 'A':
            case 'a':    make_note();break;
            case 'B':
            case 'b':    found();break;
            default :    ending();
        }
    }
}

void make_note(){
    int when;
    int day;//日期
    float zao=0, wu=0, wan=0;//早、午、晚花销
    FILE *fp;
    printf("请输入记录的日期\n");
    scanf("%d",&when);
    fp  = fopen("C:\\数据结构\\流水帐本.dat","a");
    if(fp==NULL)
    {
        printf("无法打开此文件\n");
        getch();
        exit(0);
    }
        day=when;//创建数据编号
        printf("请输入早餐费用(请输入三位数，例如xx.x)：");
        scanf("%f",&zao);
        printf("请输入午餐费用(请输入三位数，例如xx.x)：");
        scanf("%f",&wu);
        printf("请输入晚餐费用(请输入三位数，例如xx.x)：");
        scanf("%f",&wan);
        fprintf(fp,"%d%3.1f%3.1f%3.1f\n",day,zao,wu,wan);
        fclose(fp);
        system("cls");
        system("pause");
    } ;

void found()
{
    char aim[Max];
    char day[Max];
    float zao=0,wu=0,wan=0;
    data *p,*t;
    FILE *fp;
    data *Head;
    Head = (data*)malloc(sizeof(data));//为首节点分配空间
    Head->next=NULL;
    fp = fopen("C:\\数据结构\\流水帐本.dat","r");
    if(fp == NULL)
    {
        printf("无法打开此文件\n");
        exit(0);
    }
    fscanf(fp,"%s%f%f%f",day,&zao,&wu,&wan);
    Head->day=atoi(day);
    Head->price1=zao;
    Head->price2=wu;
    Head->price3=wan;
    p = Head;
    while(!feof(fp))
    {
        t=(data*)malloc(sizeof(data));
        fscanf(fp,"%s%f%f%f",day,&zao,&wu,&wan);
        t->day=atoi(day);
        t->price1=zao;
        t->price2=wu;
        t->price3=wan;
        t->next=NULL;
        p->next=t;
        p=t;
    }
    p=Head;
    fflush(stdin);
    while(1)
    {
        printf("\n输入要查询的日期：");
        scanf("%s",aim);
        for(step=0;step<8;step++)
            if(aim[step] != day[step])
            {
                p=p->next;
               
                if(p==NULL)
                {
                    printf("查无此日期的内容！");
                    break;
                }
                continue;
               
            }
            else
            {
                break;
            }
            break;
    }
    system("cls");
    printf("早餐：%3.1f\n午餐: %3.1f\n晚餐: %3.1f\n",p->price1,p->price2,p->price3);
    fclose(fp);
    //system("cls");
    system("pause");
    free(p);
    free(day);
    system("cls");
    fflush(stdin);
};//查询模块

int login()
{
    char passwords[Max+1], ch;
    int i=0;
    puts("输入密码:\n");
    while((ch = getch()) != '\r' && i < Max)
    {
        if (ch == Max)
        {
            if (i > 0)
            {
                passwords[--i] = NULL;
                printf("\b ");
                printf("%d%d%d", Max, ' ', Max);
            }
        else
            putchar(7); //bell
        }
        else
        {
            passwords[i++] = ch;
            printf("*");
        }
    }
    passwords[i] = '\0';
    if(strcmp(key,passwords_1) != 0 )
    {
        printf("密码错误！\r");
        getch();
        exit(0);
    }
    printf("\n");
    system("pause");
    system("cls");
    choice();
 
};//登陆主界面

void ending()
{
    system("cls");
        printf("            \n**************************************************************");
        printf("            \n**************************************************************");
        printf("            \n**                                                          **");
        printf("            \n**                        谢谢使用                          **");
        printf("            \n**                                                          **");
        printf("            \n**                                                          **");
        printf("            \n**************************************************************");
        printf("            \n**************************************************************");
    getch();
    exit(0);
};//结束模块

上面代码有什么错误，怎么改改？运行出来有点小问题

在线等

我觉得应该先去判断fp是不是空  然后再考虑是否打开。
然后在login函数中  passwords[--i] = NULL;这句的使用 应该不是很对

这句确实不对   不过怎么改呢？