Java大数应用

1.大数加法

 import java.math.BigInteger;
 import java.util.Scanner;

 public class Main {
     public static void main(String[] args) {
         Scanner cin = new Scanner(System.in);//大数的输入，定义一个输入器
         BigInteger a = null, b = null, c = null;//开始要赋值成空
         a = BigInteger.valueOf(100);
         b = BigInteger.valueOf(99);
         int T;
         T = cin.nextInt();//读入T;
 //        while(cin.hasNextBigInteger())//判断是否读到文件结尾相当于while(~scanf())
         for(int cas = 1; cas <= T; cas++)
         {
             a = cin.nextBigInteger();
             b = cin.nextBigInteger();

 //            BigInteger zero = BigInteger.valueOf(0);//大数判断是不是等于0
 //            if(a.equals(BigInteger.valueOf(0))){System.out.println("haha");}
 //            if(a.equals(zero)) {System.out.println("hehe");}
             c = a.add(b);
             if(cas > 1) System.out.println();//大数的换行输出
             System.out.println("Case " + cas + ":");//大数的输出是用+号连接
             System.out.println(a + " + " + b + " = "+c);
         }
         cin.close();//关闭读入器
     }

 }

2.大实数

 import java.math.BigDecimal;
 import java.util.Scanner;

 public class Main {
     public static void main(String[] args) {
     Scanner s = new Scanner(System.in);
     while(s.hasNext()){
         BigDecimal b = s.nextBigDecimal();
         BigDecimal ans = BigDecimal.valueOf(1);
         int n = s.nextInt();
         while(n-- > 0)
             ans = ans.multiply(b);
         String string = ans.stripTrailingZeros().toPlainString().toString();
         if(string.startsWith("0."))
             string = string.substring(1);
         System.out.println(string);
     }
         s.close();
     }
 }