分析：此題考絕對值函數

AC源代碼（Java語言）：

import java.util.Arrays;
import java.util.Scanner;

public class Main{
//    public final static double pi = 3.1415927;
 

    public static void main(String[] args) {
        
        Scanner sin=new Scanner(System.in);
        while(sin.hasNextDouble()){
            double num = sin.nextDouble();
            num = Math.abs(num);
            String res = String.format("%.2f", num);
            System.out.println(res);
        }
    }
}
 

HDU 2003 求絕對值