hello.java

计算以2为底的次数

package hello;
import java.io.*;
public class hello{
    public static int[] mul(int[] a, int b) { 
        int carry = 0; 
        int[] c = new int[a.length];        
        for(int i = a.length - 1; i >=0; i--) { 
            int tmp = a[i] * b + carry; 
            c[i] = tmp % 10000;    
            carry = tmp / 10000; 
        } 
        return c;
    } 
    public static void main(String[] argv) throws IOException {
        BufferedReader br = new
BufferedReader(new InputStreamReader(System.in));
        System.out.println("輸入正整數n");
        String str = br.readLine();
        int n = Integer.parseInt(str);
        int j=0;        
        int[] c = new int[50];
       c[49]=2; 
       if(n>1){
           for (j=0;j<n-1;j++){
               c=mul(c, 2);
           }
       }
        else if(n!=0){
           c[0]=2;
        }
        else{
           c[0]=1;
        }
       for(int i = 0; i < c.length; i++) { 
           if (c[i]!=0){
               System.out.print(c[i]);
           }
       }
    }
}