第二章习题

T7

public class CountE {public static void main(String args[]){int i;int n = 1;double e = 1;// 注意e取值为1而并不是0，如果是0则进入死循环，因为if语句永远不成立for (i=1; ;i++ ){n = n * i;e = e + 1.0/n;if ( Math.abs(e-2.71828) < 1e-5 )//注意取绝对值break;}System.out.println("e = "+e); }}

T8

public class ChangeArray {public static void main(String [] args){for (int i = 1; i<=9; i++){int array[] = new int[i];for (int j = 0; j<i; j++)//注意j小于而不是小于等于i，不然会使系统报错{array[j] = i*(j+1);System.out.print(i+"*"+(j+1)+"="+array[j]);System.out.print("  ");}System.out.println("");}}}

T9

public class Output {public static void main(String [] args){int a, b, i;for (a = 0; a<=7; a++){for (i=1; i<=a+1; i++){System.out.print("*");    for (b = 0; b<=a-1; b++)    {    System.out.print(".");    }}System.out.println("");}}}