##循环语句:
1.for(初始化;条件判断;迭代){
}
//先执行条件判断,后进入循环体
##2.初始化;
while(条件判断){
迭代;
}
//先执行条件判断,后进入循环体
例:
for(int i=0;i<9;i++){
}
等价于for循环与while循环等价
int i=0;
while(i<9){
i++;
}
##3.do…while();//先执行循环体,在执行条件判断
从键盘上获取一个数,判断当前的数是不是一个素数
package com.tulun.src;
import java.util.Scanner;
public class TestDemo2 {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int n = scan.nextInt();
int i;
if(n<=3) {
System.out.println(n+"是素数");
}else{
for (i = 2; i < n; i++) {
if (n % i == 0) {
break;
}
}
if(n == i) {
System.out.println(n+"是素数");
}else {
System.out.println(n+"不是素数");
}
}
}
}
有三位数100-200之间打印:”水仙花”数
package com.tulun.src;
import java.util.Scanner;
public class TestDemo2 {
//只是进行 测试:
public static void main(String[] args) {
int i;
for(i=100;i<1000;i++){
int h=i/100;
int t=(i-h*100)/10;
int u=i-h*100-t*10;
if(Math.pow(h,3) +Math.pow(t,3) +Math.pow(u,3)==i){
System.out.println(i);
}
}
}
}
##函数封装
public static viod sum(int a,int b){//参数列表 形式参数
int result = a+b;
}
public static void main(String[] args){
int a=10;局部变量
int b=20;
sum(a,b);//实际参数
}
形参是对实参进行值拷贝
判断素数
package com.tulun.src;
import java.util.Scanner;
public class Test {
/**
*
判断素数
*/
public static boolean isPrimer(int n){
boolean flag = false;
int i;
for (i = 2; i < n; i++) {
if (n % i == 0) {
break;
}
} if(n >= i) {
flag = true;
}else {
flag = false;
}
return flag;
}
public static void main (String[]args){
boolean flag = isPrimer(n);
if(flag=true){
System.out.println(n+"不是素数");
}else{
System.out.println(n+"是素数");
}
}
}
水仙花
package com.tulun.src;
import java.util.Scanner;
public class Test {
/**
* 判断水仙花数
*/
public static boolean isFlower(int n){
int result = 0;
int temp = n;
for(;temp!=0;){
int number = temp%10;
result = result+(int)Math.pow(number,3);
temp/=10;
}
if(result == n){
return true;
}
return false;
}
//变量的生命周期 定义生
public static void main (String[]args){
for(int n = 100;n<=999;n++){
boolean flag =isFlower(n);
if(flag == true){
System.out.println(n+"是水仙花数");
}
}
Scanner scan = new Scanner(System.in);
int n = scan.nextInt();
}
}
给定一个不多于9位数的正整数(几位数,输出)
package com.tulun.src;
import java.util.Scanner;
public class Test {
/**
* 给定一个不多于9位数的正整数
* 1.求这个数是几位数字
* 2.分别输出每一位数据
*/
public static int getBit(int n){
int count = 0;
while(n!=0){
n = n/10;
count++;
}
return count;
}
public static void getEveryBitNumber(int n){
int num = 0;
while(n!=0){
num=n%10;
System.out.print(num+" ");
n=n/10;
}
}
public static int reverse(int n){
int bit= getBit(n);
int num = 0;
int result = 0;
int i=0;
while(n!=0){
num=n%10;
result = result+(int)(num*Math.pow(10,bit-1-i));
// result = result+(int)(num*Math.pow(10,--bit));
n/=10;
i++;
}
return result;
}
public static void main (String[]args){
System.out.println("请输入:");
Scanner scan = new Scanner(System.in);
int number = scan.nextInt();
int bit = getBit(number);
System.out.println(bit);
getEveryBitNumber(number);
int num = reverse(number);
System.out.println(num);
}
}
斐波那契数列
package com.tulun.src;
import java.util.Scanner;
public class Test {
/**
* 斐波那契数列
*/
public static int fbnq(int n){
if(n == 1 || n == 2){
return 1;
}
int f1 = 1;
int f2 = 1;
int result = 0;
for(int i = 3;i<=n;i++){
result = f1 + f2;
f1 = f2;
f2 = result;
}
return result;
}
public static void main (String[]args){
int n = 5;
int value = fbnq(6);
System.out.println(value);
}
}
5.Sn=a+aa+aaa+aaaa+aaaaa
package com.tulun.src;
import java.util.Scanner;
public class TestDemo3{
/**
* n 由键盘输入 例如 n = 5,Sn=a+aa+aaa+aaaa+aaaaa;
* a =1;
*/
public static int sum(int a,int n){
int Sn = 0;
int temp = a;
for(int i=0;i<n;i++){
Sn = Sn + a;
a = (a * 10) + temp;
}
return Sn;
}
public static void main (String[]args){
System.out.print("请输入:"+"a = ");
Scanner scan = new Scanner(System.in);
int a = scan.nextInt();
System.out.print("请输入:"+"n = ");
int n = scan.nextInt();
int Sn =sum(a,n);
System.out.println("Sn = "+ Sn);
}
}