机试题：加减乘除

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class D_4_8_2 {

	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		String str="";
		int num1;
		String c;
		int num2 = 0;
		while((str=br.readLine())!=null)
		{
			String s[]=str.split(" ");
			num1=Integer.parseInt(s[0]);
			//System.out.println(num1);
			c=s[1];
			//System.out.println(c);
			if(!c.equals("!"))
			{num2=Integer.parseInt(s[2]);}
			//System.out.println(num2);
			if(c.equals("+"))
			{
			//	System.out.println("yes");
				System.out.println(num1+num2);
			}
			if(c.equals("-"))
			{
				System.out.println(num1-num2);
			}
			if(c.equals("*"))
			{
				System.out.println(num1*num2);
			}
			if(c.equals("/"))
			{
				if(num2==0)
				System.out.println("error");
				else
				System.out.println(num1/num2);
			}
			if(c.equals("%"))
			{
				if(num2==0)
				System.out.println("error");
				else
			    System.out.println(num1%num2);
			}
			if(c.equals("!"))
			{
				System.out.println(f(num1));
			}
		}
	}

	private static int f(int num1) {
		// TODO Auto-generated method stub
		int sum=1;
		for(int i=1;i<=num1;i++)
		{
			sum=sum*i;
		}
		return sum;
	}

}

需要注意的是!

String类的相等

不能写成：

String s;

s=="a";

而要写成

String s;

s.equals("a");