#include "stdio.h"
main()
{
    FILE *fp;
    char *p;
    char a[80];
    int i,x;
    printf("写入选1，重新写入选2，添加选3\n");
    scanf("%d",&x);
    switch(x)
    {
    case 1:if((fp=fopen("d:\\myone.txt","w"))==NULL)
    {
    printf("cann't open myone\n");
    exit(0);
    }break;
    case 2:if((fp=fopen("d:\\myone.txt","w"))==NULL)
    {
    printf("cann't open myone\n");
    exit(0);
    }break;
    case 3:if((fp=fopen("d:\\myone.txt","a"))==NULL)
    {
    printf("cann't open myone\n");
    exit(0);
    }break;
    default:printf("输入错误\n");
        exit(0);
    }
    p=a;
    printf("请输入一串字符:\n");
        for(i=0;i<5;i++)//本意我是想输入5行字符的，但第一行却为空行。
        {    gets(p);
        while(*p!='\0')
        {
            fputc(*p,fp);
                p++;
        }
        fputc('\n',fp);
        }
        fclose(fp);
}
但是当把这段注释时：
/*printf("写入选1，重新写入选2，添加选3\n");
    scanf("%d",&x);
    switch(x)
    {
    case 1:if((fp=fopen("d:\\myone.txt","w"))==NULL)
    {
    printf("cann't open myone\n");
    exit(0);
    }break;
    case 2:if((fp=fopen("d:\\myone.txt","w"))==NULL)
    {
    printf("cann't open myone\n");
    exit(0);
    }break;
    case 3:if((fp=fopen("d:\\myone.txt","a"))==NULL)
    {
    printf("cann't open myone\n");
    exit(0);
    }break;
    default:printf("输入错误\n");
        exit(0);
    }*/
添加上
if((fp=fopen("d:\\myone.txt","w"))==NULL)
    {
    printf("cann't open myone\n");
    exit(0);
    }
却能实现了``？？？
为什么呢？