Do while loop with try catch

Question

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

    InputStreamReader isr = new InputStreamReader(System.in);
    BufferedReader br = new BufferedReader(isr);

    boolean format = false;
    int grades = 0;

    do {
        System.out.println("Enter course mark (0-100): ");

        try {
            String input = br.readLine();
            grades = Integer.parseInt(input);

        } catch (NumberFormatException | IOException e) {
            System.out.println("Error number format!");
        }

    } while (!format);

    if (grades > 100 || grades < 100) {
        System.out.println("Please enter within the range (0-100)");
    }

    System.out.println("Your grades is " + grades);

}

What have i done wrong here i am trying to achieve this

Enter course mark (0-100): qwerty
Bad input data type.
Enter course mark (0-100): -12
Input out of [0, 100] range!
Enter course mark (0-100): 24
Your grades is 24

Answer 1

Change

do {
    try {
        String input = br.readLine();
        grades = Integer.parseInt(input);
    }
    catch(...) { ... }
} while (!format);

to

do {
    try {
        String input = br.readLine();
        grades = Integer.parseInt(input);
        format = true; // Add this line
    }
    catch(...) { ... } 
    if (grades > 100 || grades < 100) {
        System.out.println("Please enter within the range (0-100)");
        format = false;
    }

} while (!format);

If the execution flow reaches format = true; , then that means that the user's input was correct & will make sure that you break the input loop.

Answer 2

You no need to use the do..while block.the output is possible with While block itself. You can also change your program block like this

public static void main(String[] args) throws IOException 
{
    int grades = 0;
    InputStreamReader isr = new InputStreamReader(System.in);
    BufferedReader br = new BufferedReader(isr)
while((input=br.readLine())!=null)
    {
      try 
          {
           grades = Integer.parseInt(input);
          }
      catch (NumberFormatException | IOException e) 
          {
           System.out.println("Error number format!");
          }
    }

    if (grades > 100 || grades < 100) 
       {
        System.out.println("Please enter within the range (0-100)");
       }

 System.out.println("Your grades is " + grades);

}