java 大数加减法（小数，正负）

大数加法：

import java.math.BigInteger;  
import java.util.*;  
import java.io.*;  
  
public class Main  
{  
    public static void main(String args[])  
    {  
        Scanner in = new Scanner(System.in);  
        int n = in.nextInt();         
        for(int i = 1; i <= n; ++i)  
        {  
            BigInteger a = in.nextBigInteger();  
            BigInteger b = in.nextBigInteger();  
            BigInteger ans = a.add(b); 
            System.out.println("Case " + i + ":");  
            System.out.println(a + " + " + b + " = " +ans);  
        }  
    }  
}  

小数版

import java.math.BigDecimal;  
import java.util.*;  
import java.io.*;  

public class Main  
{  
	public static void main(String args[])  
	{  
		Scanner cin=new Scanner(System.in);
		while(cin.hasNext()){
			String s=cin.next();
			String ss=cin.next();
			BigDecimal a=new BigDecimal(s);
			BigDecimal b=new BigDecimal(ss);
			BigDecimal t=a.add(b);
			System.out.println(t);
		}
	}  
}  

大数减法：

import java.math.BigInteger;  
import java.util.*;  
import java.io.*;  
  
public class Main  
{  
    public static void main(String args[])  
    {  
        Scanner in = new Scanner(System.in);  
        int n = in.nextInt();         
        for(int i = 1; i <= n; ++i)  
        {  
            BigInteger a = in.nextBigInteger();  
            BigInteger b = in.nextBigInteger();  
            b=b.negate();//把b变成负的
            BigInteger ans = a.add(b); 
            System.out.println("Case " + i + ":");  
            System.out.println(a + " + " + b + " = " +ans);  
        }  
    }  
}