Scanner cleared during loop: how do I still maintain a certain condition? - loops

Question

I am in the process of making a program which will display 3 problems of operation type which a user picks. I've used a loop to keep the program generating random numbers for each iteration as well as to display another problem. The problem I'm having is in trying to clear the scanner after taking user input as to not keep the wrong value stored and screw up the loop. I need the one value ("a") to be stored so that the loop continues with the next question. For this post I've taken out all options but addition just for debugging purposes. My code I will paste below:
public static void main(String[] args) {
Scanner stdin = new Scanner(System.in);
Random randGen = new Random(Config.RANDOM_SEED);
// Welcome
System.out.println("Hello and welcome to the Math Trainer!\n======================================");
System.out.println("Which math operation would you like to practice?");
// Create a counter for correct answers
int correctCount = 0;
// Create a for loop to generate multiple questions
for (int count = 0; count < Config.NUMBER_OF_QUESTIONS; count++) {
// Calculate random values from seed and shift them within range
int ran1 = randGen.nextInt(Config.MAX_VALUE - Config.MIN_VALUE + 1);
int ran2 = randGen.nextInt(Config.MAX_VALUE - Config.MIN_VALUE + 1);
int ran1Shift = ran1 + Config.MIN_VALUE;
int ran2Shift = ran2 + Config.MIN_VALUE;
// Initialize different answers per operation
double additionAnswer = (double) ran1Shift + ran2Shift;
double subtractionAnswer = (double) ran1Shift - ran2Shift;
double multiplicationAnswer = (double) ran1Shift * ran2Shift;
double divisionAnswer = (double) ran1Shift / ran2Shift;
double remainderAnswer = (double) ran1Shift % ran2Shift;
// Ask for user input on which to choose (only on first run of loop)
if (count == 0) {
System.out.println(" " + "[A]ddition");
System.out.println(" " + "[S]ubtraction");
System.out.println(" " + "[M]ultiplication");
System.out.println(" " + "[D]ivision");
System.out.println(" " + "[R]emainder");
System.out.print("Enter your choice:" + " ");
}
// Presentation of addition problems
if (stdin.nextLine().equalsIgnoreCase("a")) {
System.out.print(
"What is the solution to the problem:" + " " + ran1Shift + " " + "+" + " " + ran2Shift + " = ");
if (stdin.hasNextDouble()) {
double userNum = stdin.nextDouble();
stdin.nextLine();
if (userNum == additionAnswer) {
System.out.println("That is correct!");
correctCount++;
} else {
System.out.println("The correct solution is: " + additionAnswer + ".");
}
} else {
stdin.nextLine();
System.out.println("All solutions must be entered as decimal numbers.");
System.out.println("The correct solution is " + additionAnswer + ".");
}
} else {
System.out.println("I'm sorry, I only understand choices of: A, S, M, D, or R!");
count--;
}
}
// Program exit
System.out.println("*** You answered " + correctCount + " out of 3 questions correctly. ");
System.out.println("======================================");
System.out.println("Thank you for using the Math Trainer!");
}
}
The output I get if I enter the correct answer to the first problem (13) is:
https://gyazo.com/773f9be3b51f51f5086f38f36ed0c86b
In which I have to enter "a" again for the next question to show.
The output I should get is here:
https://gyazo.com/6609a9f0b44d0b446439d3331be51eb9
Please let me know if you have any questions and thank you very much for your help.

Answer 1

if (stdin.nextLine().equalsIgnoreCase("a")) this is the cause of your problem.
For a quick fix, move the codes asking for operationType to outside of the loop since it's only executed once.
System.out.println(" " + "[A]ddition");
System.out.println(" " + "[S]ubtraction");
System.out.println(" " + "[M]ultiplication");
System.out.println(" " + "[D]ivision");
System.out.println(" " + "[R]emainder");
System.out.print("Enter your choice:" + " ");
String operationType = stdin.nextLine();
for (int count = 0; count < Config.NUMBER_OF_QUESTIONS; count++) {
//codes
if (operationType.equalsIgnoreCase("a")) {
Might be better to use a switch statement for checking the operationType too.