循环语句
循环语句
do-while循环和while循环：do-while语句先执行循环体一次，然后判断循环继续条件
循环体：循环中重复执行的语句部分称为循环体
do-while和while语句：通常用于循环次数不确定的情况
for循环：一般用于循环次数已知的情况
break：立即终止包含break的最内层循环
continue：终止当前迭代
while(循环继续条件){
循环体
语句；
}
do{
循环体；
语句；
}while(循环继续条件)
for(初始条件；循环继续条件；每次执行完循环体后的操作){
循环体；
语句；
}
嵌套循环：
package day04;
public class Test4_3 {
public static void main(String[] args) {
for(int i=1;i<=6;i++){
for(int j=1;j<=i;j++){
System.out.print("*");
}
System.out.print('\n');
}
}
}
//
// *
// **
// ***
// ****
// *****
// ******
package day04;
public class Test4_3 {
public static void main(String[] args) {
for(int i=6;i>=1;i--){
for(int j=1;j<=i;j++){
System.out.print("*");
}
System.out.print('\n');
}
System.out.println("--------------------");
for(int i=1;i<=11;i++){
for(int j=1;j<=i&&(i+j)<=12;j++){
System.out.print('*');
}
System.out.println();
}
System.out.println("--------------------");
for(int i=1;i<=9;i++){
for(int j=1;j<=Math.abs(i-5);j++){
System.out.print(" ");
}
for(int k=1;k<=i&&(k+i<=10);k++){
System.out.print("* ");
}
System.out.println();
}
System.out.println("--------------------");
//
//
for(int i=1;i<=11;i++){
for(int j=1;j<=i&&(i+j)<=12;j++){
System.out.print('*');
}
System.out.println();
}
System.out.println("--------------------");
for(int i=1;i<=9;i++){
for(int j=1;j<=Math.abs(i-5);j++){
System.out.print(" ");
}
for(int k=1;k<=i&&(k+i)<=10;k++){
if(k==1||k+i==10||k==i){
System.out.print("* ");
}else{
System.out.print(" ");
}
}
System.out.println();
}
}
}
******
*****
****
***
**
*
--------------------
*
**
***
****
*****
******
*****
****
***
**
*
--------------------
*
* *
* * *
* * * *
* * * * *
* * * *
* * *
* *
*
--------------------
*
**
***
****
*****
******
*****
****
***
**
*
--------------------
*
* *
* *
* *
* *
* *
* *
* *
*
编程练习：
/*
* 读入整数的个数不确定
* 正数个数
* 负数的个数
* 计算数的总和、平均值（浮点数）
* 输入为0 程序结束
* */
import java.util.Scanner;
public class Demo4_1{
public static void main(String[] args){
Scanner scanner = new Scanner(System.in);
System.out.print("Enter an interger,the input ends if it is 0:");
int zhengshu=0;
int fushu=0;
int count=0;
double sum=0;
while(true){
int number = scanner.nextInt();
sum+=number;//sum=sum+number;
count++;
if(number>0){
zhengshu++;
}else if(number<0){
fushu++;
}else if(count==1&&number==0){
System.out.println("No numbers are entered except 0");
}
else{
count--;
System.out.println("The number of positives is "+zhengshu);
System.out.println("The number of negatives is "+fushu);
System.out.println("The total is "+sum);
System.out.println("The average is "+sum/count);
return;
}
}
}
}
/*
* 用户输入学生的个数
* 姓名和分数
* 显示：
* 最高分 姓名
* 次高分 姓名
* */
import java.util.Scanner;
public class Demo4_2 {
public static void main(String[] args) {
String theBestname = "";//最高分的姓名
String theSecondname = "";//次高分的姓名
double theBestGrade = 0;//最高分
double theSecondGrade = 0;//次高分
Scanner scanner = new Scanner(System.in);
System.out.println("Enter the number of students:");
int number = scanner.nextInt();
while(number>0){
System.out.println("Enter the name of student: ");
String name = scanner.next();
System.out.println("Enter the grade of student: ");
double grade = scanner.nextDouble();
number--;
if(grade>theBestGrade){
theSecondGrade = theBestGrade;
theSecondname = theBestname;
theBestGrade = grade;
theBestname = name;
}else if(grade<theBestGrade){
if(grade>theSecondGrade){
theSecondGrade = grade;
theSecondname = name;
}
}
}
System.out.println("姓名和最高分："+theBestname +" "+theBestGrade);
System.out.println("姓名和次高分："+theSecondname+" "+theSecondGrade);
}
}
/*
* 100<=number<=200
* number%5==0
* number%6==0
* 不能被5和6同时整除
* 10数为一行
* */
public class Demo4_3 {
public static void main(String[] args) {
int count = 0;
for(int number=100;number<=200;number++){
if((number%5==0||number%6==0)&&(!(number%5==0&&number%6==0))){
System.out.print(number+" ");
count++;
if(count%10==0){
System.out.println();
}
}
}
}
}
public class Demo4_4 {
public static void main(String[] args) {
int n=1;
while(n*n<=12000){
n++;
}
System.out.println(n);
System.out.println("=========");
int m=1;
while(m*m*m<=12000){
m++;
}
m=m-1;
System.out.println(m);
}
}
import java.util.Scanner;
public class Demo4_5 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the number:");
int number = scanner.nextInt();
while(true){
boolean flag = false;
for(int i=2;i<=number/2;i++){
if(number%i==0){
System.out.print(i+" ");
number/=i;
flag=true;
break;
}
}
if(!flag){
System.out.println(number);
break;
}
}
}
}
4.6
import java.util.Scanner;
public class Demo4_6 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Enter the line:");
int line = scanner.nextInt();
for(int i=1;i<=line;i++){
for(int k=1;k<=line-i;k++){
System.out.print(" ");
}
for(int j=-i;j<=i;j++){
if(j!=0&&j!=1){
System.out.printf("%3d",Math.abs(j));
}
}
System.out.println();
}
}
}
import java.util.Scanner;
public class Demo4_8 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Enter the line:");
int line = scanner.nextInt();
for(int i=1;i<=line;i++){
for(int k=1;k<=line-i;k++){
System.out.print(" ");
}
for(int j=-(i-1);j<=(i-1);j++){
if(j<=0){
System.out.printf("%4d",(int)Math.pow(2,j+i-1 ));
}else{
System.out.printf("%4d",(int)Math.pow(2, -j+i-1));
}
}
System.out.println();
}
}
}
public class Demo4_10 {
public static void main(String[] args) {
double PI = 1.0;
//方法一：
// for(int i=1;i<=10000;i++){
// if(i%2==1){
// PI = PI-1.0/(2*i+1);
// }else{
// PI = PI+1.0/(2*i+1);
// }
// }
// 方法二：
// double flag = -1.0;
// for(int i=1;i<=10000;i++){
// PI = PI+flag/(2*i+1);
// flag = -flag;
// }
// 方法三：
for(int i=1;i<=10000;i++){
PI = PI-Math.pow(-1, i+1)/(2*i+1);
}
PI*=4;
System.out.println(PI);
}
}
public class Demo4_11 {
public static void main(String[] args) {
double e=1.0;
for(int i=1;i<=10000;i++){
double res=1;
for(int j=1;j<=i;j++){
res*=j;
}
e=e+1/res;
}
System.out.println(e);
}
}
public class Demo4_12 {
public static void main(String[] args) {
int count = 0;
for(int i=101;i<=2100;i++){
if(i%4==0&&i%100!=0||i%400==0){
System.out.print(i+" ");
count++;
if(count%10==0){
System.out.println();
}
}
}
System.out.println("\n"+count);
}
}
import java.util.Scanner;
public class Demo4_13 {
public static void main(String[] args) {
int year;
int week;
Scanner scanner = new Scanner(System.in);
year = scanner.nextInt();
week = scanner.nextInt();
int m,y,k,j,h;
String monthStr="";
String weekStr="";
for(int month = 1;month<=12;month++){
m=month;
y=year;
if(m==1||m==2){
m+=12;
y--;
}
k=y%100;
j=y/100;
h=(1+26*(month+1)/10+k+k/4+j/4+5*j)%7;
switch(month){
case 1:
monthStr = "January";
break;
case 2:
monthStr = "February";
break;
case 3:
monthStr = "March";
break;
case 4:
monthStr = "April";
break;
case 5:
monthStr = "May";
break;
case 6:
monthStr = "June";
break;
case 7:
monthStr = "July";
break;
case 8:
monthStr = "Augest";
break;
case 9:
monthStr = "September";
break;
case 10:
monthStr = "October";
break;
case 11:
monthStr = "November";
break;
case 12:
monthStr = "December";
break;
}
switch(h){
case 0:
weekStr = "Sunday";
break;
case 1:
weekStr = "Monday";
break;
case 2:
weekStr = "Tuesday";
break;
case 3:
weekStr = "Wednessday";
break;
case 4:
weekStr = "Thursday";
break;
case 5:
weekStr = "Friday";
break;
case 6:
weekStr = "Saturday";
break;
}
System.out.println(monthStr+" 1, "+year+" is "+weekStr);
}
}
}
public class Demo4_15{
public static void main(String[] args) {
int sum=0;
for(int i=1;i<=10000;i++){
for(int j=1;j<=i/2;j++){
if(i%j==0){
sum+=j;
}
}
if(sum==i){
System.out.println(sum);
}
sum=0;
}
}
}
import java.util.Scanner;
public class Demo4_16 {
public static void main(String[] args) {
int pCount=0;
int cCount=0;
Scanner scanner = new Scanner(System.in);
while(true){
System.out.println("请输入：0:剪刀 1:石头 2:布");
int c = scanner.nextInt();
int p = (int)(Math.random()*3);
if(c==p){
System.out.println("平局，请继续！");
}
if(p==0&&c==1){
System.out.println("电脑赢");
cCount++;
}
if(p==0&&c==2){
System.out.println("玩家赢");
pCount++;
}
if(p==1&&c==0){
System.out.println("玩家赢");
pCount++;
}
if(p==1&&c==2){
System.out.println("电脑赢");
pCount++;
}
if(p==2&&c==0){
System.out.println("电脑赢");
pCount++;
}
if(p==2&&c==1){
System.out.println("玩家赢");
pCount++;
}
if(pCount==2||cCount==2){
break;
}
}
if(pCount==2){
System.out.println("最终玩家获胜！");
}else{
System.out.println("最终电脑获胜！");
}
}
}
public class Demo4_17 {
public static void main(String[] args) {
double sum=0;
for(int i=1;i<=624;i++){
sum=sum+1.0/(Math.sqrt(i)+Math.sqrt(i+1));
}
System.out.println(sum);
}
}
import java.util.Scanner;
public class Demo4_18 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("请输入一个十进制整数：");
int number = scanner.nextInt();
String str = "";
// while(true){
//// 十进制到二进制
// str = number%2+str;
// number/=2;
// if(number==0){
// break;
// }
// }
// System.out.println(str);
// while(true){
//// 十进制到八进制
// str = number%8+str;
// number/=8;
// if(number==0){
// break;
// }
// }
// System.out.println(str);
while(true){
int num = number%16;
if(num>=10){
switch(num){
case 10:
str="A"+str;
break;
case 11:
str="B"+str;
break;
case 12:
str="C"+str;
break;
case 13:
str="D"+str;
break;
case 14:
str="E"+str;
break;
case 15:
str="F"+str;
break;
}
}else{
str=num+str;
}
number/=16;
if(number==0){
break;
}
}
System.out.println("0X"+str);
}
}
4.19
import java.util.Scanner;
public class Demo4_19 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Enter numbers:");
int max=0;
int count=0;
while(true){
int number = scanner.nextInt();
if(number==0){
break;
}
if(number>max){
max=number;
count=1;
}else if(number==max){
count++;
}
}
System.out.println("The largest number is:"+max);
System.out.println("The occurrence count of the largest number id :"+count);
}
}
public class Demo4_20 {
public static void main(String[] args) {
int count=0;
for(int i=1;i<=7;i++){
for(int j=i+1;j<=7;j++){
System.out.println(i+" "+j);
count++;
}
}
System.out.println("The total number of all combinations id :"+count);
}
}
import java.util.Scanner;
public class Demo4_21 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
double sum=0;
double powsum=0;
System.out.println("Enter 10 numbers:");
for(int i=1;i<=10;i++){
double num = scanner.nextDouble();
sum+=num;
powsum+=num*num;
}
double mean = sum/10;
double sd = Math.sqrt(powsum-sum*sum/10)/9;
System.out.println("mean:"+mean);
System.out.println("sd:"+sd);
}
}
import java.util.Scanner;
public class Demo4_22 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Enter the first string:");
String s1 = scanner.nextLine();
System.out.println("Enter the second string:");
String s2 = scanner.nextLine();
int i=0;
for(;i<=Math.min(s1.length(), s2.length());i++){
if(s1.charAt(i)!=s2.charAt(i))
break;
}
System.out.println("["+s1.substring(0,i)+"]");
}
}
4.23
import java.util.Scanner;
public class Demo4_23 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Enter a string:");
String str = scanner.nextLine();
int i=0;
int count=0;
for(;i<str.length();i++){
if(str.charAt(i)>=65&&str.charAt(i)<=90){
count++;
}
}
System.out.println(count);
}
}
import java.util.Scanner;
public class Demo4_24 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Enter the String:");
String str = scanner.nextLine();
for(int i=0;i<str.length();i++){
if(i%2==0){
System.out.print(str.charAt(i));
}
}
}
}