java控制结构

Java 基础及控制结构练习题1.有一函数⎪⎩⎪⎨⎧≤-<≤+<=xx x x x x y 30103303523 写一程序，输入x,输出y 值。

import java.util.Scanner;public class JavaApplication4 {public static void main(String[] args) {int x, y = 0;Scanner sc = new Scanner(System.in);x = sc.nextInt();if (x >= 30) {y = 3 * x - 10;}if (x >= 3 && x < 30) {y = 2 * x + 5;}if (x < 3) {y = x;}System.out.println("y=" + y);}}2.编程从键盘上输入任意两个整数给变量x 和y ，使用两种方法交换x 和y 的值(方法一：a=a+b; b=a-b;a=a-b; 方法二：a=a^b;b=b^a;a=a^b)import java.util.Scanner;public class JavaApplication4 {public static void main(String[] args) {int x = 0, y = 0;Scanner sc = new Scanner(System.in);x = sc.nextInt();System.out.println("x=" + x);y = sc.nextInt();System.out.println("y=" + y);System.out.println("x,y 交换后：");f(x, y);}static void f(int x, int y) {int m = x;x = y;y = m;System.out.println("x=" + x);System.out.println("y=" + y);}}3.从键盘上输入三角形的三边a,b,c，先判断它们是否能构成一个三角形，如果是则计算三角形的面积。

import java.util.Scanner;public class JavaApplication10 {public static void main(String[] args) {int x, y, z, s, area;Scanner sc = new Scanner(System.in);System.out.print("a=");x = sc.nextInt();System.out.print("b=");y = sc.nextInt();System.out.print("c=");z = sc.nextInt();if (f(x, y, z)) {System.out.println("是三角形！");s = (x + y + z) / 2;area = s * (s - x) * (s - y) * (s - z);area = (int) Math.sqrt(area);System.out.println("三角形的面积为：" + area);} else {System.out.println("不是三角形！");}}static boolean f(int a, int b, int c) {if (a + b > c && b + c > a && a + c > b) {return true;} else {return false;}}}4.从键盘上输入一个大于10的整数，1）判断它是几位数？2）求各位上数字和；3）判断哪个位上存在数字4？import java.util.Scanner;public class JavaApplication4 {public static void main(String[] args) {int x, sum = 0, t, i;Scanner sc = new Scanner(System.in);System.out.print("x=");x = sc.nextInt();System.out.println(x);if (x <= 10) {System.out.print("输入错误！");System.exit(0);}for (i = 1; x > 0; x = x / 10, i++) {t = x % 10;sum = sum + t;if (t == 4) {System.out.println(i + "位上存在4！");}}System.out.println("x 是" + (i - 1) + "位数");System.out.println("各位上数字和：" + sum);}}5.编程计算： (11)6957453321++++++的前30项的和，要求保留3位小数位。

public class JavaApplication10 {public static void main(String[] args) {double x, y, z, s, area = 0;for (double i = 1.0; i <= 30; i++) {area = area + i / (2 * i - 1);}System.out.println("算式的答案为：" + area);}}6.编程计算1!+2!+3!+.....+n!。

n 从键盘输入。

import java.util.Scanner;public class JavaApplication9 {public static void main(String[] args) {long sum = 0, t, i, j;Scanner sc = new Scanner(System.in);System.out.print("n=");n = sc.nextInt();for (i = 1; i <= n; i++) {t = 1;for (j = 1; j <= i; j++) {t = t * j;}sum = sum + t;}System.out.println("1!+2!+3!...+n!=" + sum);}}7.从键盘上输入一个正整数m，找出1000至10000之间所有各位数字之和等于m的数。

如输入32,则有9869满足要求。

因为9869各位上数字之和等于32。

import java.util.Scanner;public class JavaApplication9 {public static void main(String[] args) {int n, a;Scanner sc = new Scanner(System.in);System.out.print("n=");n = sc.nextInt();f(n);}static void f(int n) {int i, sum, m, t, s = 0;for (i = 1000; i <= 10000; i++) {sum = 0;for (m = i; m > 0; m = m / 10) {t = m % 10;sum = sum + t;}if (sum == n) {System.out.print(i + " ");s++;if (s % 5 == 0) {System.out.println();}}}}8.从键盘上输入一个正整数n,求出5位数中各位数字之和等于n的所有素数,每行按6个素数输出。

import java.util.Scanner;public class JavaApplication9 {public static void main(String[] args) {int n, a;Scanner sc = new Scanner(System.in);System.out.print("n=");n = sc.nextInt();f(n);}static void f(int n) {int i, sum, m, q, c, k = 0;for (i = 10000; i <= 99999; i++) {sum = 0;for (m = i; m > 0; m = m / 10) {sum = sum + m % 10;}if (sum == n) {q = (int) Math.sqrt(i);for (c = 2; c < q; c++) {if (i % c == 0) {break;}}if (c >= q) {System.out.print(i + " ");k++;if (k % 6 == 0) {System.out.println();}}}}}}9.编程求下式的值：n1+n2+n3+n4+…+n10，其中n=1,2,3。

编写函数时，设置参数n的默认值为2。

import java.util.Scanner;public class JavaApplication9 {public static void main(String[] args) {int n = 2, a;Scanner sc = new Scanner(System.in);System.out.print("n=");n = sc.nextInt();System.out.println("n1+n2+n3+n4+…+n10=" + f(n));}static int f(int n) {int i, t = 1, sum = 0, j;for (i = 1; i <= 10; i++) {for (j = 1; j <= i; j++) {t = t * n;}sum = sum + t;}return sum;}}10.给定求组合数公式为：C n m = m!/ n! (m-n)!编一程序，输入m 和n的值import java.util.Scanner;public class JavaApplication9 {public static void main(String[] args) {int n, m;Scanner sc = new Scanner(System.in);System.out.print("n=");n = sc.nextInt();System.out.print("m=");m = sc.nextInt();System.out.println("Cnm = m!/ n! (m-n)!=(m>n)" + f(n, m)); }static int f(int n, int m) {int i, t = 1, sum = 0, a = 1, b = 1;if (m < n) {System.out.println("输入错误！！");System.exit(0);}for (i = 1; i <= n; i++) {t = t * i;}for (i = 1; i <= m; i++) {a = a * i;}sum = m - n;for (i = 1; i <= sum; i++) {b = b * i;}sum = a / (t * b);return sum;}}11.求s=1+（1+2）+（1+2+3）+…….+（1+2+3+……+n）的值。