void enter_mima(char *enter_1)
{
    int j=0,i=0;
    char ch;
    for(;;)
    {
        ch=getch();
        if(j==0)//输入密码的首字符
        {
            if((int)ch==13)//如果是回车键
            {
                printf("请输入密码");
            }
            else
            {
                if((int)ch==8)//如果是退格键
                {     
                *enter_1='\0';//这个键怎么去实现呢？看不懂  实现是这个键也用不了     
                }
                else
                {
                    j=1;
                    *enter_1=ch;//这里也能详细说明下就好了
                    enter_1++;
                    i++;
                    printf("*");
                }
            }
        }
        else//密码首字符之后的字符
        {
            if(i>=15&&(int)ch!=13&&(int)ch!=8)
            {
                *enter_1='\0';
            }
            else if((int)ch==8)
            {
                if(i>0)//****************
                {
                    i--;
                    enter_1--;
                    *enter_1='\0';
                }
                else
                {
                    j=0;
                    *enter_1='\0';
                }//**********************
            }
            else if((int)ch==13)
            {
                break;
            }
            else
            {
                *enter_1=ch;
                enter_1++;
                i++;
                printf("*");
            }
        }
    }
    *enter_1='\0';
    printf("\n");
}

用printf("\b \b");可以实现退格删除的效果
至于*enter_1=ch;就是将输入的字符存到enter_1当前指向的位置