循环语句及双重循环

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复习：

//1！+2！+3！+………+9！+10！=sum
public class Test {
public static void main(String[] args) {
int a=1;
int sum=0;
for (int i =1; i <=10; i++) {
a*=i;//a=a*i;
sum+=a;
}
System.out.println(sum);
}
}

双重循环，即一个循环内嵌着另外一个循环，外面的循环每跑一遍，内循环均要全部跑完。

练习1：

//利用双循环打印倒三角
public class Test1 {
public static void main(String[] args) {
for (int i = 15; i > 0; i--) {
for (int j = 0; j < i; j++) {
System.out.print("*");
}
System.out.println();
}
}

}

练习2：

//正三角
public class Test2 {
public static void main(String[] args) {
for (int i = 1; i < 10; i++) {
for (int j = 0; j < i; j++) {
System.out.print("*");
}
System.out.println();
}
}
}

练习3：

//菱形
public class Test3 {
public static void main(String[] args) {

int hangshu = 11;
int yiban = hangshu / 2 + 1;
int yibanduo = hangshu / 2;
System.out.println("空心菱形：");
for(int k = 1;k <= yiban;k++){
for(int i = 1;i <= (yiban - k);i++){
System.out.print(" ");
}
System.out.print("*");
for(int i = 1;i <= ( (k - 2) * 2 + 1);i++){
System.out.print(" ");
}
if(k != 1){
System.out.print("*");
}
System.out.println();
}
for(int k = yibanduo;k >=1;k--){
for(int i = 1;i <= (yiban - k);i++){
System.out.print(" ");
}
System.out.print("*");
for(int i = 1;i <= ( (k - 2) * 2 + 1);i++){
System.out.print(" ");
}
if(k != 1){
System.out.print("*");
}
System.out.println();
}

System.out.println("实心菱形：");
for(int i = 1;i <= hangshu;i++){
if(i <= hangshu/2 + 1){
for(int k = 1;k <= hangshu/2 + 1- i;k++){
System.out.print(" ");
}
for(int k = 1;k <= i;k++){
System.out.print("* ");
}
System.out.println();
}else{
for(int k =1;k <= (i -(hangshu/2 + 1));k++){
System.out.print(" ");
}
for(int k = 1;k <= (2 *(hangshu/2 + 1) - i);k++){
System.out.print("* ");
}
System.out.println();
}
}
}
}

练习4：

public class Test4 {
/**
* 等腰三角形
*/
public void print1(){//形如 ▲向上的
for(int i=1;i<=5;i++){
for(int k=1;k<=5-i;k++)
System.out.print(" ");
for(int j=1;j<=2*i-1;j++)
System.out.print("*");

System.out.print("\n");
}
}

public void print2(){//形如：倒▲ 向下的
for(int i=1;i<=5;i++){
for(int j=1;j<=i-1;j++)
System.out.print(" ");
for(int k=1;k<=11-(2*i);k++)
System.out.print("*");

System.out.print("\n");
}
}

public static void main(String[] args) {
Test4 app = new Test4();
System.out.println

("---------------------------");
app.print1();
System.out.println

("---------------------------");
app.print2();
System.out.println

("---------------------------");
}
}

练习5：数组复习

import java.util.Scanner;

//从控制台接收数据，用数组存储并计算姓张的人数
public class Test5 {
public static void main(String[] args) {
String name []=new String[5];
int sum=0;
for (int i = 0; i < name.length; i++) {
Scanner scr=new Scanner(System.in);
System.out.println("第"+(i+1)+"位姓名：");
name[i]=scr.next();
}
for (int i = 0; i < name.length; i++) {

if (name[i].startsWith("张")) {
sum++;
}
}
System.out.println("姓张的人数为:"+sum);
}

}

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