int num=0;
do{
System.out.print("请选择,输入数字:");
num= input.nextInt();
if(num>4||num<1){
System.out.print("输入错误,请重新输入数字:");
num=input.nextInt();
}else{
switch(num){
case 1:
System.out.println(op1);
break;
case 2:
System.out.println(op2);
break;
case 3:
System.out.println(op3);
break;
case 4:
System.out.println(op4);
break;