If a user inputs an invalid character how can I get my program to output a message to the user and re ask the question?

1

Hi,

In my java program, if the user enters the wrong character such as “E” or “A” in my program how can I output a message to the user? The line which I’m speaking about in my program is when the user has to choose to input one out of three characters P, M or D. However, if the user inputs another character which isn’t listed I want the program to display a message.

As you can see if the user inputs “E” the program skips to the next step. However, I want the user to be notified and asked again to enter the correct value which is “P, M or D”.

In order to do what I’m trying to achieve I believe I need to do an if statement so here what I have tried.

if((i = P,M,D) && (i < ?)) {
   System.out.println("ERROR, please input only P,M or D.");
}

Screenshot of the program

JAVA CODE

        String grade;
        int yr2cred[] = new int[18];
        char yr2grade[] = new char[18];
        for (int i = 1; i <= 18; i++) {
            System.out.println("Please enter your grade for unit " + i +" "+(username) + ".");
            grade = userinput.next();
            yr2grade[i - 1] = grade.charAt(0);
            if (yr2grade[i - 1] == 'P' || yr2grade[i - 1] == 'p') {
                yr2cred[i - 1] = yr2cred[i - 1] + P;
            }
            if (yr2grade[i - 1] == 'M' || yr2grade[i - 1] == 'm') {
                yr2cred[i - 1] = yr2cred[i - 1] + M;
            }
            if (yr2grade[i - 1] == 'D' || yr2grade[i - 1] == 'd') {
                yr2cred[i - 1] = yr2cred[i - 1] + D;
            }
        }
2

perhaps a dropdown menu, with options to force the input to be correct if that’s a possibility - or maybe some sort of while loop…

do {
 get new input
 if (inputInvalid) {
   "display an invalid message" 
 } 
} while (inputInvalid)

i know that’s pretty vague but it’s not nothing

3

I think the DO-WHILE loop fits the best for your case.
The code for it would be something like:

do {
    // get the userinput
} 
while (input != 'P' || input != 'M' || input != 'D');

The loop will iterate again and again until the condition inside the while loop is met . i.e until the preferred character is inputted. Then it will exit the loop and go to the following lines of code.

4

Hi, any chance you can put my code into the DO-WHILE loop as I keep getting error for some reason? Thanks for your feedback post.

5 
do {
    System.out.println("Provide your input");
    grade = userinput.next();
}
while (grade != 'P' || grade != 'M' || grade != 'D');

This is the general pattern and it should work on java as well.

Btw I dont know what is with your link . You are writing java in Html file. Moreover, I guess jsfiddle is just for javascript.