java学习笔记3

5. 多重循环和程序调试

5.1 多重循环

多重循环是指循环中嵌套循环结构
多重循环注意事项
- 各种循环可以互相嵌套
- 一般不要超过三层嵌套
- 外层循环变化一次，内层循环要全部执行完

代码

**需求1：**使用循环嵌套输出10*10的矩形

java">  public static void demo() {for (int i = 0; i < 10; i++) {System.out.print("第" + (i + 1) + "行: ");for (int j = 0; j < 10; j++) {System.out.print("*");}System.out.println("");}}

**需求2：**输出n层的直角三角形

java">  public static void demo() {Scanner sc = new Scanner(System.in);System.out.println("输入直角三角形的高: ");int n = sc.nextInt();if (n < 0) {System.out.println("三角形的层高不能为负数！");// 终止正在执行的函数，return后面的语句不会再执行return;}// 外层循环控制行for (int i = 0; i < n; i++) {// 内层循环控制*个数for (int j = 0; j <= i; j++) {System.out.print("*");}// 输出*结束，换行System.out.println();}}

**需求3：**输出倒n层的直角三角形

java">  public static void demo() {Scanner sc = new Scanner(System.in);System.out.println("输入直角三角形的高: ");int n = sc.nextInt();for (int i = 0; i < n; i++) {for (int j = 0; j < n - i; j++) {System.out.print("*");}System.out.println();}}

**需求4：**输出n层靠右直角三角形

java">  public static void demo() {Scanner sc = new Scanner(System.in);System.out.println("输入直角三角形的高: ");int n = sc.nextInt();// 行for (int i = 0; i < n; i++) {// 左边空格for (int k = 0; k < n - i - 1; k++) {System.out.print(" ");}// *for (int j = 0; j <= i; j++) {System.out.print("*");}// 换行System.out.println();}}

**需求5：**输出n层平行四边形

java">  public static void demo() {Scanner sc = new Scanner(System.in);System.out.println("输入平行四边形的高: ");int n = sc.nextInt();// 行for (int i = 0; i < n; i++) {// 空格for (int j = 0; j < n - i - 1; j++) {System.out.print(" ");}// *for (int j = 0; j < n; j++) {System.out.print("*");}// 换行System.out.println();}}

**需求6：**输出n层等腰三角形

java">  public static void demo() {Scanner sc = new Scanner(System.in);System.out.println("输入三角形的高: ");int n = sc.nextInt();for (int i = 0; i < n; i++) {// 空格for (int j = 0; j < n - i - 1; j++) {System.out.print(" ");}// *for (int j = 0; j < 2 * i + 1; j++) {System.out.print("*");}// 换行System.out.println();}}

需求7： 9*9乘法表

java">  public static void task() {for (int i = 1; i <= 9; i++) {for (int j = 1; j <= i; j++) {System.out.print(i + " × " + j + " = " + (i * j) + "\t");}System.out.println();}}

**需求8：**输出数字金字塔

java">  public static void task() {Scanner sc = new Scanner(System.in);System.out.println("输入一个整数(1-9):");int n = sc.nextInt();for (int i = 0; i < n; i++) {// 空格for (int j = 0; j < n - i - 1; j++) {System.out.print(" ");}// 数字for (int j = 0; j < 2 * i + 1; j++) {System.out.print(i + 1);}// 换行System.out.println();}}

**需求9：**n层菱形

java">public static void task() {Scanner sc = new Scanner(System.in);System.out.println("输入菱形的高:");int h = sc.nextInt();if (h <= 0) {System.out.println("菱形的高是正整数！");return;}// 如果是偶数，层高+1h = h % 2 == 0 ? ++h : h;// 获得当前菱形的上半部分的高int up = h / 2 + 1;int down = up - 1;System.out.printf("up=%d,down=%d\n", up, down);// 输出上半部分for (int i = 0; i < up; i++) {// 空格for (int j = 0; j < up - i - 1; j++) {System.out.print(" ");}// 输出*for (int j = 0; j < 2 * i + 1; j++) {if (j == 0 || j == 2 * i) {System.out.print("*");} else {System.out.print(" ");}}// 换行System.out.println();}// 输出下半部分for (int i = 0; i < down; i++) {// 空格for (int j = 0; j <= i; j++) {System.out.print(" ");}// 输出*for (int j = 0; j < 2 * down - 2 * i - 1; j++) {System.out.print("*");}System.out.println();}}

**需求10：**一只公鸡值5元，一只母鸡值3元，而1元可买3只小鸡。现有100元钱，把钱正好花完，正好买到100只鸡。请问可买公鸡、母鸡、小鸡各几只

java">  public static void task() {// 公鸡的个数for (int i = 0; i < 21; i++) {// 母鸡的个数for (int j = 0; j < 34; j++) {// 小鸡的个数/* for (int k = 0; k < 101; k++) {// 3只小鸡1元，一只小鸡是 1/3.0元，k只是 k/3.0元if (i * 5 + 3 * j + k / 3.0 == 100 && (i + k + j) == 100) {System.out.println("公鸡有：" + i + "只，母鸡有：" + j + "只,小鸡有：" + k);}}*/int k = 100 - j - i;if (i * 5 + 3 * j + k / 3.0 == 100) {System.out.println("公鸡有：" + i + "只，母鸡有：" + j + "只,小鸡有：" + k);}}}}

**需求11：**鸡兔同笼问题：上面数，有35个头，从下面数，有94只脚。问笼中各有多少只鸡和兔？

java">  public static void task() {for (int i = 0; i <= 35; i++) {/*for (int j = 0; j <= 94; j++) {if (i + j == 35 && i * 2 + j * 4 == 94) {System.out.println("鸡有" + i + "只,兔有" + j + "只");}}*/int j = 35 - i;if (i * 2 + j * 4 == 94) {System.out.println("鸡有" + i + "只,兔有" + j +