【Java】1.判断成绩，2.判断闰年，3.运算符，4.输入三个正整数（不超过int类型表示的最大范围），输出这三个数字中最大值， 5. 有一个函数： 写程序，输入x的值，输出y相应的值

1.判断成绩

package com.tulun.src;
import java.util.Scanner；
public class TestDemo {
public static void main(String[] args){
System.out.println("请输入成绩");
Scanner scanner = new Scanner(System.in);
int grade =scanner.nextInt();
if(grade<60){
System.out.println('D');
}else if(grade>=60&&grade<=75){
System.out.println("C");
}else if(grade>75&&grade<85){
System.out.println("B");
}else{
System.out.println("A");
}
}
}

2.判断闰年

package com.tulun.src;
import java.util.Scanner;
public class TestDemo {
public static void main(String[] args){
System.out.println("请输入年份");
Scanner scanner = new Scanner(System.in);
int year = scanner.nextInt();
if(year%4==0 && year%100 != 0){
System.out.println(year+"是闰年");
}else if(year%100 ==0 && year%400==0){
System.out.println(year+"是闰年");
}else{
System.out.println(year+"不是闰年");
}
}
}

3.运算符

package com.tulun.src;
import java.util.Scanner;
public class TestDemo {
public static void main(String[] args){
int a=0;
int b=a--;
System.out.println(a+""+b);//-1  0
b=--a;
System.out.println(a+""+b);//-2  -2
b=a--;
System.out.println(a+""+b);//-3，-2
b=++a;
System.out.println(a+""+b);//-2，-2
a++;
b=a--;
System.out.println(a+""+b);// -2  -1
}
}

4.输入三个正整数（不超过int类型表示的最大范围），输出这三个数字中最大值。

package com.tulun.src;
import java.util.Scanner;
public class TestDemo {
public static void main(String[] args){
Scanner scanner = new Scanner(System.in);
int a = scanner.nextInt();
int b = scanner.nextInt();
int c = scanner.nextInt();
if(a>=b) {
if (a >= c) {
System.out.println("最大值为" + a);
} else {
System.out.println("最大值为" + c);
}
}else if(b>=c){
System.out.println("最大值为"+b);
}else{
System.out.println("最大值为"+c);
}
}
}

优化：

package com.tulun.src;
import java.util.Scanner;
public class TestDemo {
public static void main(String[] args){
Scanner scanner = new Scanner(System.in);
int a = scanner.nextInt();
int b = scanner.nextInt();
int c = scanner.nextInt();
int max = (a>b?a:b) >c ?(a>b?a:b):c;
System.out.println("最大值为" + max);
}
}

1. 有一个函数： 写程序，输入x的值，输出y相应的值

package com.tulun.src;
import java.util.Scanner;
public class TestDemo {
public static void main(String[] args){
Scanner scanner = new Scanner(System.in);
int x = scanner.nextInt();
int y;
if(x<1){
System.out.println(y=x);
}else if(x>=1 && x<10){
System.out.println(y=2*x-1);
}else {
System.out.println(y=3*x-11);
}
}
}

优化:

package com.tulun.src;
import java.util.Scanner;
public class TestDemo {
public static void main(String[] args){
Scanner scanner = new Scanner(System.in);
int x = scanner.nextInt();
int y;
if(x<1){
return y;
}else if(x>=1 && x<10){
return y;
}else if(x>=10) {
return y;
}
System.out.println(y);
}
}