循环结构

循环结构

while循环

package com.xw.struct;

public class WhileD01 {
    public static void main(String[] args) {
        //输出1~100
        int i = 0;
        while (i<100){//i>100就停止循环
            i++;
            System.out.println(i);
        }
    }
}

package com.xw.struct;

public class WhileD02 {
    public static void main(String[] args) {
        //计算1+2+3+...+100
        int i = 0;
        int sum =0;
        while (i<=100){
        sum =sum +i;
        i++;
        }
        System.out.println(sum);
    }
}

while先判断后执行

do...while

package com.xw.struct;

public class DoWhileD01 {
    public static void main(String[] args) {
        //1+2+3...+100
        int i = 0;
        int sum =0;
        do {
            sum =sum +i;
            i++;
        }while (i<=100);
        System.out.println(sum);//5050
    }
}

package com.xw.struct;

public class Dowhile02 {
    public static void main(String[] args) {
        int a = 0;
        while (a<0){
            a++;
            System.out.println(a);//不会被输出
        }
        System.out.println("==============================");
        do {
            System.out.println(a);//0
            a++;
        }while (a<0);
        System.out.println(a);//1
    }
}

do...while先执行后判断

for循环

package com.xw.struct;

public class ForD01 {
    public static void main(String[] args) {
        //初始化//条件判断//迭代 
        for (int  i = 0;  i <= 100;  i++) {
            System.out.println(i);
        }
    }
}

package com.xw.struct;

public class ForD02 {
    public static void main(String[] args) {
        //计算0~100奇数和，偶数和
        int a= 0;//奇数和
        int b =0;//偶数和
        for (int i = 0;i<=100;i++){
            if (i%2!=0){
                a+=i;//a=a+i
            }else {
                b+=i;//b=b+i
            }
        }
        System.out.println(a);//奇数和
        System.out.println(b);//偶数和
        System.out.println(a+b);//1~~100总和
    }
}

用for循环

package com.xw.struct;

public class ForD03 {
    public static void main(String[] args) {
        //用while或者for循环输出1~1000之间能被5整除的数,且每行输出3个
        for (int i = 1; i <= 1000; i++) {
            if (i%5==0){//i/5的余数为0
                System.out.print(i+"\t");
            }if (i%(5*3)==0){//输出3个后
                System.out.println();//换行或者  System.out.print("\n")
                //System.out.println();输出完会换行
                //System.out.print();输出完不会换行
            }
        }
    }
}

用while循环

package com.xw.struct;

public class ForD04 {
    public static void main(String[] args) {
        int a =0;
        while (a<=1000){
            a++;
        if (a%5==0){
            System.out.print(a+"\t");
        }if (a%(5*3)==0) {
                System.out.println();
            }
        }
    }
}

九九乘法表

package com.xw.struct;

public class ForD05 {
    public static void main(String[] args) {
        //打印九九乘法表
        for (int i = 1; i <= 9; i++) {//定义i为1~9
            for (int j = 1; j <= i; j++) {//定义j永远小于或者等于 i   1~9
            System.out.print(j+"*"+i+"="+(j*i)+"\t");//打印  j*i=(j*i)
            }
            System.out.println();
        }
    }
}

增强for循环

package com.xw.struct;

public class ForD06 {
    public static void main(String[] args) {
          int[] a ={10,20,30,40,50  };//定义一个数组 a
        for (int i = 0; i<5;i++){
            System.out.println(a[i]);
        }
        System.out.println("======================");
        for (int b :a){//遍历数组的元素
            System.out.println(b);
        }
    }
}

打印三角形

package com.xw.struct;

public class Text01 {
    public static void main(String[] args) {
        //打印一个三角形
        for (int i = 1; i <=5; i++) {//i=1~5
            for (int j = 5; j >=i; j--) {//5 4 3 2 1
                System.out.print(" ");
            }
            for (int j= 1; j<=i ;j++){// 1 2 3 4 5
                System.out.print("*");
            }
            for (int k = 1; k < i; k++) {//0 1 2 3 4
                System.out.print("*");
            }
            System.out.println();//5“ ”+   1“*”+  0“*”
        }
    }
}

理解型

package com.xw.struct;

public class Text001 {
    public static void main(String[] args) {
        System.out.println("      *");
        System.out.println("     ***");
        System.out.println("    *****");
        System.out.println("   *******");
        System.out.println("  *********");
    }
}