循环（九）

循环（九）

while和do-whlie循环

package com.luca.structs;

public class WhileDemo1 {
    public static void main(String[] args) {
        //计算1到100的总和
        int i = 0;
        int sum = 0;
        while (i<=100) {
            sum += i;
            i++;
        }
        System.out.println(sum);

        //do while和while的区别：dowhile至少会执行一次语句，而while条件不成立则会立即跳出
        int i2 = 0;
        int sum2 = 0;
        do {
            sum2 += i2;
            i2++;
        } while (i2<=100);
        System.out.println(sum2);
    }
}

for循环

package com.luca.structs;

public class ForDemo1 {
    public static void main(String[] args) {
        //使用for输出1到100的和
        int sum = 0;
        for (int i = 0; i <= 100; i++) {
            sum += i;
        }
        System.out.println(sum);
        System.out.println("================");

        //输出1到100中的奇数和与偶数和
        int oddsum = 0;
        int evensum = 0;
        for (int i = 0; i <= 100; i++) {
            if (i % 2 == 0) {
                evensum += i;
            } else {
                oddsum += i;
            }
        }
        System.out.println("奇数和是：" + oddsum);
        System.out.println("偶数和是：" + evensum);
        System.out.println("================");

        //输出1-100中所有5的倍数，并且三个为一行显示
        for (int i = 1; i <= 100; i++) {
            if (i % 5 == 0) {
                System.out.print(i + " ");
            }
            if (i % 15 == 0) {
                System.out.println();
            }
        }
        System.out.println();
        System.out.println("================");

        //打印九九乘法表
        for (int i = 1; i <= 9; i++) {
            for (int j = 1; j <= i; j++) { //注意这里的j<=i
                System.out.printf("%d*%d=%d ", i, j, i * j);
            }
            System.out.println();
        }
        System.out.println("================");

        //增强型for循环
        int[] m = {1, 2, 3, 4, 5}; //定义一个数组，相当于python的list
        for (int x: m) {
            System.out.print(x+"\t"); //这里的\t需要用双引号括起来，用单引号的话会有问题
        }
    }
}

上面for循环输入结果如下：

使用for循环打印一个三角形

现在打印的三角形比较丑，是将打印拆分成三个部分拼起来

package com.luca.structs;

public class ForDemo02 {

    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            //打印最左边的空白三角
            for (int j = 5; j >= i; j--) {
                System.out.print(" ");
            }
            //打印中间的半个三角形
            for (int j = 1; j<=i; j++) {
                System.out.print("*");
            }
            //打印右边的半个三角形
            for (int j = 5; j > (5-i); j--) {
                System.out.print("*");
            }

            System.out.println();
        }
    }
}

Break和Continue

Break：跳出循环结构

package com.luca.structs;

public class BreakDemo {
    public static void main(String[] args) {
        int i = 0;
        while (i<10) {
            i++;
            if (i==5) {
                break; //如果i=5，会跳出循环结构
            }
            System.out.println(i);
        }
        System.out.println("It's over.");
    }
}

Continue：跳出本次循环

package com.luca.structs;

public class ContinueDemo {
    public static void main(String[] args) {
        //break continue goto/label
        int i = 0;
        while (i < 10) {
            i++;
            if (i==5){
                continue; //如果i=5，则跳出本次循环，继续下一轮循环
            }
            System.out.println(i);
        }
    }
}