Checking if a number entered is odd

`I'm not sure what code to insert or even where, but I would like to check the number I enter is an odd number.

import java.io.*;
import javax.swing.JOptionPane;

public class Diamond {
    public static void main(String [] args) throws IOException {

        BufferedReader stdin = new BufferedReader (new InputStreamReader (System.in));
        String input; 
        int num;
        System.out.println("input number: ");
        input = stdin.readLine ();
        num = Integer.parseInt(input);开发者_如何学JAVA

        if (num % 2 ==1){
            int d = num;
            int e = 0;
            for (int a = 0; a <= num; a++) {
                for (int c = d; c>= 1; c-- )
                    System.out.print(" ");
                d-=1;
                for (int b = 1; b <= a; b++)
                    System.out.print ("* ");
                System.out.println();
            }

            num-=1;
            for (int a = 0; a<=num; a++) {
                for (int b = num; b > a; b--)
                    System.out.print (" *"); 
                System.out.println(); 
                for (int c = 0; c <= e; c++)
                    System.out.print(" ");
                 e+=1;
            }
        } else {
            System.out.println("Please enter an odd number!");
        }
    }
}

Use modular arithmetic:

if (number % 2 == 0) {
  // even
} else {
  // odd
}

Update:

You can test this code here:

• https://repl.it/Hkc6/1

Beware that checking for evenness with number % 2 == 1 will fail.

To check if a number is odd, you can use (number & 1) != 0.

num % 2 == 1 return incorrect results on negative Odd number, the remainder of division with 2 will not be 1. This can be fixed as follows:

public boolean isOddNumber(int num) {
    return (num & 1) != 0;
}

You can NOT have readLine inside of that if. First you need to get the value and next you can use your if.

It goes like this:

BufferedReader stdin = new BufferedReader (new InputStreamReader (System.in));

String input; 
int num;

System.out.println("input number: ");

  input = stdin.readLine();
  num = Integer.parseInt(input);

if (num % 2 == 1) {
// odd
} else {
  System.out.println("Please enter an odd number!");
}

Finally - do NOT use values named "a", "e" or "d" - it's very confusing. Just name vars with names that let reader know/guess their role in your code. I have no idea what is the meaning of your "a" or b, c, d etc. For example, your num should be named enteredValue to clarify your code.

Chaker's answer about negative integer is confirmed. In my JavaSE-1.8

System.out.println( "result =" + ( -3 % 2 == 1) );

it shows result =false instead true

Bitwise operation (bit manipulation) way in Java

if ((num & 1) != 0) //odd
{
     //do something here
} else { //even
    //do something here
}

works by looking at say, 100 (number 4) vs 001, doing the AND operation on each bits and returning either 0 and 1. If the end bit is a 0, like 4, it's always going to be even. If the end bit is 1, it is going to be odd.