在int型范围内，打印
（1）求N!
（2）求N!-M!
(3) 求N!+M!
package demo05;
import java.util.ArrayList;
import java.util.Scanner;
public class JieCheng {
public static void main(String[] args) {
while(true){
boolean bl = false; //判断change方法中是否执行打印操作
System.out.println("请选择你要的操作：");
System.out.println("1、计算N的阶乘");
System.out.println("2、计算N!+M!的和");
System.out.println("3、计算N!-M!的差（M>N）");
System.out.println("4、退出");
Scanner input = new Scanner(System.in);
int c = input.nextInt();
switch(c){
case 1 :
System.out.println("请输入N的值：");
Scanner num = new Scanner(System.in);
int number = num.nextInt();
bl=true;
change(number,bl);
break;
case 2 :
System.out.println("请输入N和M的值：(N
Scanner num1 = new Scanner(System.in);
int n = num1.nextInt();
int m = num1.nextInt();
sum(change(n,bl),change(m,bl));
break;
case 3 :
System.out.println("请输入N和M的值：(N
Scanner x = new Scanner(System.in);
int y = x.nextInt();
int z = x.nextInt();
minus(change(y,bl),change(z,bl));
break;
case 4 :
System.out.println();
System.out.println();
System.out.println();
System.out.println("good-bye!");
return;
}
}
}
/**
* 计算输入数字的阶乘，并转存在数组中
*/
public static ArrayList
ArrayList list = new ArrayList();
list.add(1);
for(int i=2;i<=num;i++){
int c = 0;
for(int j = 0;j
int p = list.get(j)*i+c;
list.set(j, p%10);
c=p/10;
}
while(c>0){
list.add(c%10);
c=c/10;
}
}
if(bl==true){
for(int j = list.size();j>0;j--){
System.out.print(list.get(j-1));
}
System.out.println();
bl=false;
}
return list;
}
public static void sum(ArrayList n ,ArrayList m){
ArrayList s = new ArrayList();
int c = 0; //存在进位值
int i= 0; //存储的是所用元素的角标
for(i = 0;i
int temp = n.get(i)+m.get(i)+c;
s.add(i, temp%10);
c=temp/10;
}
while(i<=m.size()-1)
{
int temp=m.get(i)+c;
s.add(i,temp%10);
c/=10;
i++;
}
for(int j = s.size();j>0;j--){
System.out.print(s.get(j-1));
}
System.out.println();
}
/**
* 拿大数减小数，结果加负号
*/
public static void minus(ArrayList n ,ArrayList m){
ArrayList min = new ArrayList();
int c = 0 ; //借位值
int i = 0;
for(i = 0;i
int temp = m.get(i)-n.get(i)+c;
if(temp>=0){
min.add(i, temp);
c=temp/10;
}else if(temp<0){
min.add(i,temp+10);
c=-1;
}
}
while (i
int temp = m.get(i)+c;
if(temp>0){
min.add(i, temp);
i++;
c=0;
}else if(temp==0){
min.add(i, temp);
i++;
c=0;
}else if (temp<0){
min.add(i,9);
c=-1;
i++;
}
}
System.out.print("-");
for(int j = min.size();j>0;j--){
System.out.print(min.get(j-1));
}
System.out.println();
}
}
欢迎大家拍砖，指正！