Java what's wrong here

[oliverjrose99]

the loop runs even if operation is right, what am i doing wrong

import java.util.Scanner;public class Main {	public static void main(String[] args) {		//Create object for Scanner		Scanner input = new Scanner(System.in);				//Create variables		int answer, fnum, snum, num;		String operation;				//Operation loop		do {			 System.out.println("Operations:\n+\n-\n*\n/\nEnter the operation:");			 operation = input.nextLine();			 			 if (operation != "+" && operation != "-" && operation != "*" && operation != "/") {				 System.out.println("\nNot a valid operation, Try again...");			 }		} while (operation != "+" && operation != "-" && operation != "*" && operation != "/");				System.out.println("Done...");	}}

[fletch to 99]

A do-while loop will always execute once because the check is performed after the loop is executed. Do this... check  if we still should do it... do it again... etc.

 

Your probably wanting a while loop...

while Condition...do this

You can read more about it here: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/while.html

[oliverjrose99]

this wont work

while (operation != "+" && operation != "-" && operation != "*" && operation != "/") {	System.out.println("Operations:\n+\n-\n*\n/\nEnter the operation:");	operation = input.nextLine();	if (operation != "+" && operation != "-" && operation != "*" && operation != "/") {		System.out.println("Not a valid operation, Try again...");	}}

[WanderingFool]

Your first post was almost right....the big thing is != and == are insanely misleading in java.  != and == compares objects, so strings get messed up with != and ==.

 

For strings, and other objects don't use ==, instead use .equals

 

so your code

import java.util.Scanner;public class Main {	public static void main(String[] args) {		//Create object for Scanner		Scanner input = new Scanner(System.in);				//Create variables		int answer, fnum, snum, num;		String operation;				//Operation loop		do {			 System.out.println("Operations:\n+\n-\n*\n/\nEnter the operation:");			 operation = input.nextLine();			 			 if (!operation.equals("+") && !operation.equals("-") && !operation.equals("*") && !operation.equals("/")) {                         //As another note, when this condition happens you will get the text printing out, but you will also exit the while loop                         //so you will end up it printing not a valid operation and then printing done....but I will let you fix that				 System.out.println("\nNot a valid operation, Try again...");			 }		} while (!operation.equals("+") && !operation.equals("-") && !operation.equals("*") && !operation.equals("/"));				System.out.println("Done...");	}}

[oliverjrose99]

 

Your first post was almost right....the big thing is != and == are insanely misleading in java.  != and == compares objects, so strings get messed up with != and ==.

 

For strings, and other objects don't use ==, instead use .equals

 

so your code

import java.util.Scanner;public class Main {	public static void main(String[] args) {		//Create object for Scanner		Scanner input = new Scanner(System.in);				//Create variables		int answer, fnum, snum, num;		String operation;				//Operation loop		do {			 System.out.println("Operations:\n+\n-\n*\n/\nEnter the operation:");			 operation = input.nextLine();			 			 if (!operation.equals("+") && !operation.equals("-") && !operation.equals("*") && !operation.equals("/")) {                         //As another note, when this condition happens you will get the text printing out, but you will also exit the while loop                         //so you will end up it printing not a valid operation and then printing done....but I will let you fix that				 System.out.println("\nNot a valid operation, Try again...");			 }		} while (!operation.equals("+") && !operation.equals("-") && !operation.equals("*") && !operation.equals("/"));				System.out.println("Done...");	}}

thanks alot, im new to java