Simple Java Program Strange Output

Question

This is my program...

import java.lang.Math;
class SquareRoot
{
  public static void main(String args[])
  {
    try
    {
      System.out.println("Enter A Number To Find its Square Root");
      System.out.flush();
      double x = (double) System.in.read();
      double y;
      y = Math.sqrt(x);
      System.out.println("Square Root of " + x + " is " + y);
    }
    catch (Exception e)
    {
      System.out.println("I/O Error! Humein Maaf Kar Do Bhaaya");
    }
  }
}

If I enter 75 as input it shows.. Square Root of 55.0 is <55's square root>
On entering 23 it shows Square Root of 50.0. Where am I wrong? No problems in compilation.

I am using DrJava IDE. JDK 7u25 Compiler. Windows 7 32 bit.

User input is done wrong. Use a Scanner instead of System.in directly. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Aug 8, 2013 at 15:13
import java.lang.Math isn't needed, the java.lang package is implicitly imported — BackSlash
– BackSlash, Commented Aug 8, 2013 at 15:18

RiaD · Accepted Answer · 2013-08-08 15:20:01Z

8

System.in.read() returns one character. Then its integer representation casted to double.

You may use BufferedReader:

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String s = br.readLine();
double number = Double.parseDouble(s);

Or Scanner:

Scanner scanner = new Scanner(System.in);
double number = scanner.nextDouble();

edited Aug 8, 2013 at 15:20

answered Aug 8, 2013 at 15:14

RiaD

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1 Comment

Luiggi Mendoza Over a year ago

Or Scanner for simplicity of code and avoid parsing String to the data I want/need.

christopher · Accepted Answer · 2013-08-08 15:26:25Z

4

double x = (double) System.in.read();

Nope. I would recommend wrapping this up in a Scanner.

Scanner s = new Scanner(System.in);
double x = s.nextDouble();
String str = s.nextLine(); // <-- Just an example!

Just makes for much nicer code!

Remember

Put import java.util.Scanner at the top of your page, otherwise Java will kick up a bit of a fuss!

edited Aug 8, 2013 at 15:26

answered Aug 8, 2013 at 15:15

christopher

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6 Comments

BackSlash Over a year ago

There is no need to assign s.nextLine() to a string if you are using it just to empty the buffer

christopher Over a year ago

I was just using that as an example of it's usage.

GunJack Over a year ago

What is String str for?

christopher Over a year ago

Just an example of it's usage. Wow I didn't think it would be this confusing :P

RiaD Over a year ago

@GunJack did you import java.util.Scanner?

|

StephenTG · Accepted Answer · 2013-08-08 15:14:29Z

2

The problem is that when you are casting as a double when getting the user input, it is converting the first character in the input into its ascii value. ('7' = 55, '2' = 50)

answered Aug 8, 2013 at 15:14

StephenTG

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Comments

Shamim Ahmmed · Accepted Answer · 2013-08-08 15:17:23Z

1

Use follows:

Scanner s = new Scanner(System.in);
double x = s.nextDouble();

edited Aug 8, 2013 at 15:17

answered Aug 8, 2013 at 15:16

Shamim Ahmmed

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