嘁,都2020了,你咋还在单纯的使用if-else

//C语言代码片段
int Days(int months, int years){
	int days;
	if(months==1 || months==3 || months==5 || months==7 || months==8 || months==10 || months==12){
		days=31;
	}else if(months==2){
		if((years%4==0 && years%100!=0) || years%400==0){
			days=29;
		}else{
			days=28;
		}
	}else if(months==4 || months==6 || months==9 || months==11){
		days=30;
	}else{
		printf("输入错误！请重新输入：\n");
		Days(months,years);
	}
	return days;
}

//c++代码片段
class Solution {
public:
  bool isPowerOfTwo(int n) {
  	//如果一个数是 2 的次方数的话，那么它的二进数必然是最高位为1，其它都为 0 ，
  	//那么如果此时我们减 1 的话，则最高位会降一位，其余为 0 的位现在都为变为 1，
  	//那么我们把两数相与，就会得到 0
    return (n > 0) && (!(n & (n - 1)));
  } 
};

//java代码片段
public class Solution {
  public int trailingZeroes(int n) {
  	//不断递归
    return n == 0 ? 0 : n / 5 + trailingZeroes(n / 5);
  }
}

goodswitch(age){
	case 10:
		break;
	case 20:
		break;
	case 30:
		break;
	//...
}

//javascript 语法片段
const month=new Date().getMonth(),
	year=new Date().getFullYear(),
	isLeapYear=year%4==0 && year%100!=0 || year%400==0;

const monthDays=[31,isLeapYear ? 29 : 28,31,30,31,30,31,31,30,31,30,31];
const days=monthDays[month];

//JavaScript 语法片段
ages=[10,20,...];
funs=['a1','a2',...];
for(let i in ages){
	if(age==ages[i]){
		funs[i]();
	}
}
function a1(){
}
function a2(){
}
//...

//TypeScript 语法片段
const Age={
	0:"unadult",
	1:"adult"
}
const Gender={
	0:"female",
	1:"male"
}
const Marry={
	0:"unmarried",
	1:"married"
}

const rateMap={
	[Age[0]+Gender[0]+Marry[0]]:0.1,
	[Age[0]+Gender[0]+Marry[1]]:0.2,
	[Age[0]+Gender[1]+Marry[1]]:0.3,
	[Age[0]+Gender[1]+Marry[0]]:0.4,
	[Age[1]+Gender[0]+Marry[0]]:0.5,
	[Age[1]+Gender[0]+Marry[1]]:0.6,
	[Age[1]+Gender[1]+Marry[1]]:0.7,
	[Age[1]+Gender[1]+Marry[0]]:0.8
}
const isAdult=(age:number)=>age>=18 ? 1: 0
const getDate=(age,hasMarried,gender)=>{
	age=isAdult(age)
	return rateMap[Age[age]+Gender[gender]+Marry[marry]]
}

//TypeScript 语法片段
const ageRanges:number[]=[17,65,100],
	keys:string[]=['<18','18-65','>65'];
const getKey=(age:number):string=>{
	for(let i in keys){
		//console.log(i);
		//console.log(ageRanges[i]);
		if(age<=ageRanges[i]){
			return keys[i];
		}
	}
	return keys[keys.length-1];
}

//Typescript 代码片段
const ages:string[]=['<18','<18','<18',...'18-65','18-65','18-65',...'>65','>65','>65',...'>65'];
const ageKey:string=ages[age];

//JavaScript 代码片段
const keys=['A','B','C','D','E','F','G','H'],
	range=[45,90,135,180,225,270,315,360];
const degreeTkey=(rage)=>{
	for(let i in range){
		if(rage<=range[i]){
			return keys[i];
		}
	}
}
const map={
	'A':()=>{
		//...
	},
	'B':()=>{
		//...
	},
	//...
}

//调用如：
map[degreeTkey(46)]();

public interface RoleOperation {
  String op();//表示某个角色可以做哪些op操作
}

public enum RoleEnum implements Role0peration {
  //系统管理员(有A操作权限)
	ROLE_ ROOT_ _ADMIN {
		@Override
		public String op() {
			return "ROLE_ ROOT_ ADMIN:" + " has AAA permission";
		}
	},
	//订单管理员(有B操作权限)
	ROLE_ ORDER_ ADMIN {
		@override
		public String op() {
			return "ROLE_ ORDER_ _ADMIN:" + " has BBB permission";
		}
	},
	//普通用户(有C操作权限)
	ROLE_ NORMAL {
	@Override
		public String op() {
			return "ROLE_ NORMAL:" + "has CCC permission";
		}
	};
}

public class JudgeRole {
	public String judge( String roleName ) {
		//一行代码搞定!之前的if/else没了!
		return RoleEnum.va1ue0f(roleName).op();
	}
}

//系统管理员(有A操作权限)
public class RootAdminRole implements Role0peration {
	private String roleName ;
	public RootAdminRole( String roleName){
		this.roleName = roleName ;
	}
	@Override
	public String op() {
		return roleName + "has AAA permission" ;
	}
}

//订单管理员(有B操作权限)
public class OrderAdminRole implements RoleOperation {
	private String roleName ;
	public OrderAdminRole( String roleName ) {
		this.roleName = roleName ;
	} 
	@Override
	public String op() {
		return roleName + "has BBB permission";
	}
}

//普通用户(有C操作权限)
public class NormalRole implements RoleOperation {
	private String roleName ;
	public NormalRole( String roleName){
		this.roleName = roleName;
	}
	@Override
	public String op() {
		return roleName + "has CCC permission";
	}
}

public class RoleFactory {
	static Map<String, Role0peration> roleOperationMap = new HashMap<>();
	//在静态块中先把初始化工作全部做完
	static {
		role0perationMap.put( "ROLE_ ROOT_ ADMIN", new RootAdminRole("ROLE_ _ROOT_ ADMIN") ) :
		roleOperationMap.put( "ROLE_ ORDER_ ADMIN", new OrderAdminRole("ROLE_ ORDER_ ADMIN") );
		role0perationMap.put( "ROLE_ NORMAL", new NormalRole("ROLE_ NORMAL") );
	}
	pub1ic static RoleOperation getOp( String roleName ) {
		return roleOperationMap.get( roleName ) ;
	}
}

public class JudgeRole {
	public String judge(String roleName){
		//一行代码搞定!  之前的if/else也没了!
		return RoleFactory.get0p(roleName).op();
	}
}