如何定制输入6个字符，多输入一下系统响应嘟的警告音？
定长输入字符串，同时验证必须为字符和数字还有下划线，其他字符非法。怎么实现？我的代码不能阻止过多输入字符！

[解决办法]
仅供参考

C/C++ code

#include <conio.h>#include <stdio.h>char pw[40];int i,ch;FILE *f;void main() {    cprintf("\r\nPassword:");    i=0;pw[i]=0;    while (1) {        ch=getch();        if (ch==13) break;        if (i>=39) {            cprintf("\a");            continue;        }        switch (ch) {        case 27:            cprintf("\rPassword: %40s"," ");            cprintf("\rPassword: ");            i=0;pw[i]=0;            break;        case 8:            if (i>0) {                i--;                pw[i]=0;                cprintf("\b \b");            }            break;        default:            pw[i]=ch;            i++;            pw[i]=0;            cprintf("*");            break;        }    }    cprintf("\r\n");    f=fopen("password.txt","w");    fprintf(f,"%s\n",pw);    fclose(f);}
[解决办法]
响铃(bell)    \a