while loop not working as expected

[Biodun Adeniji]

I am a beginner. I'm trying to write a program that accepts a score from its user, displays a corresponding grade and asks if the user wants to continue(loop). The loop aspect is not working.

import java.util.Scanner;

public class newGrade
{
	public static void main(String[]args)
	{
	int score; 
	boolean res = false;
	
	
	Scanner input = new Scanner (System.in);
	
	System.out.print("Enter a score: ");
	score = input.nextInt();
	
	do
	
	 {
	
	if(score >= 70)
	System.out.print("Your grade is A");
	else if(score >= 60)
	System.out.print("Your grade is B");
	else if(score >= 50)
	System.out.print("Your grade is C");
	else if(score >= 45)
	System.out.print("Your grade is D");
	else if(score >= 40)
	System.out.print("Your grade is E");
	else if(score < 40)
	System.out.print("Your grade is F");
	System.out.print("\nDo you want  to continue?(1 = yes/2 = no): ");
	res = input.nextBoolean();
	} while (res = false);
	
	}
}

[Tehmina Yaseen]

Just put that code in main methods it's working fine now

int score;
 boolean flag=false;
    int res = 0;
    Scanner input = new Scanner (System.in);
    do
     {
            System.out.print("Enter a score: ");
    score = input.nextInt();
    if(score >= 70)
    System.out.print("Your grade is A");
    else if(score >= 60)
    System.out.print("Your grade is B");
    else if(score >= 50)
    System.out.print("Your grade is C");
    else if(score >= 45)
    System.out.print("Your grade is D");
    else if(score >= 40)
    System.out.print("Your grade is E");
    else if(score < 40)
    System.out.print("Your grade is F");
    
    System.out.print("\nDo you want  to continue?(1 = yes/2 = no): ");
    res = input.nextInt();
    if(res == 1)
    {
        flag = true;
    }
    else
        flag= false;
    } while(flag);
    }

[Carey Brown]

input.nextBoolean() is expecting either the string "true" or the string "false".

[Jesper de Jong]

It doesn't work because you are using an assignment instead of a comparison in line 34:

	} while (res = false);

What you are doing here is setting the variable res to false, instead of just checking if it is false. Comparison is done with == instead of =:

	} while (res == false);

Better yet: Use the ! operator (the "not" operator) and do it like this:

	} while (!res);

[Campbell Ritchie]

The error with = false shows why you shouldn't use == false or == true.

By the way: that isn't a while loop; it is a do loop (or a do‑while loop). There is a subtle difference between the two, whih youwill doubtless find explained in the Java™ Tutorials.