C#有关循环体和goto

试试这样:
BankClient clientX = null;

while (null == clientX)
{
Console.WriteLine("请输入姓名：");
name = Console.ReadLine();
switch (name)
{
case "张三": clientX = clientA; break;
case "李四": clientX = clientB; break;
case "王五": clientX = clientC; break;
case "赵六": clientX = clientD; break;
default: Console.WriteLine("没有这个用户！"); break;
}
}

……
BankClient clientX;

bool flag = false;
while(true)
{
Console.WriteLine("请输入姓名：");
name = Console.ReadLine();
switch (name)
{
case "张三": clientX = clientA; break;
case "李四": clientX = clientB; break;
case "王五": clientX = clientC; break;
case "赵六": clientX = clientD; break;
default: Console.WriteLine("没有这个用户！"); flag=true; break;
}
if(flag == false)
break;
}

Console.WriteLine("请输入密码：");
……

把goto a;
换成
Console.WriteLine("请输入姓名：");
name = Console.ReadLine();
然后再把上面的a:去掉就行了