I'm self learning java for a few weeks and started testing my (basic) knowledge. So, i was trying to create something like some formulas calculator, with an index selector. I wanna know if its possible to, after using a formula, go back to the first question. I tryied to use a while loop but couldn't figure it out.
Thanks for the help.
João Silva
public class formulas {
public static void main(String[] args) {
// TODO Auto-generated method stub
// first question
// constant values definition
final double PI = 3.141592653589793238;
//index
ArrayList<String> index = new ArrayList<>();
index.add("1. Pythagorean Theorem");
index.add("2. Square Area");
index.add("2. Triangle Area");
System.out.println("Formulas Index:");
System.out.println("");
for(int i=0; i<index.size(); i ) {
System.out.println(index.get(i));
}
System.out.println("");
System.out.print("Write the formulas number you want to use: ");
Scanner scanner = new Scanner(System.in);
String firstQuestion = scanner.nextLine();
System.out.println();
// methods selection
if (firstQuestion.equals("1")) {
System.out.println("Pythagoras Theorem");
System.out.print("Insert side a: ");
double a = scanner.nextDouble();
System.out.print("Insert side b: ");
double b = scanner.nextDouble();
double c = pitagoras(a,b);
System.out.println("Hypotenuse c: " c);
}
else if (firstQuestion.equals("2")) {
System.out.println("Square area");
System.out.print("Insert side a: ");
double arestaA = scanner.nextDouble();
System.out.print("Insert side b: ");
double arestaB = scanner.nextDouble();
double squareArea = squarearea(arestaA,arestaB);
System.out.println("The square area is: " squareArea);
}
else System.out.println("Please insert a valid formula number.");
}
// methods parameters
static double pitagoras(double a, double b) {
double c = Math.sqrt((a*a) (b*b));
return c;
}
static double squarearea(double a, double b) {
double area = a*b;
return area;
}
}
CodePudding user response：
I'm always surprised that people don't make more use of do-while loops, it's a severely underrated construct.
Think about it, you MUST do at least one iteration of the loop before you know if you want to continue or exit the loop. You also want to re-print the menu on each iteration, so it's easier to just put it in a do-while (IMHO)
You can take a look at Control Flow Statements and The while and do-while Statements for more details
import java.util.ArrayList;
import java.util.Scanner;
public final class Main {
public static void main(String[] args) {
// TODO Auto-generated method stub
// first question
// constant values definition
final double PI = 3.141592653589793238;
//index
ArrayList<String> index = new ArrayList<>();
index.add("1. Pythagorean Theorem");
index.add("2. Square Area");
index.add("3. Triangle Area");
index.add("4. Quit");
boolean printMenu = true;
boolean exit = false;
do {
if (printMenu) {
System.out.println("");
System.out.println("Formulas Index:");
System.out.println("");
for (int i = 0; i < index.size(); i ) {
System.out.println(index.get(i));
}
System.out.println("");
System.out.print("Write the formulas number you want to use: ");
}
printMenu = true;
Scanner scanner = new Scanner(System.in);
String firstQuestion = scanner.nextLine();
System.out.println();
// methods selection
if (firstQuestion.equals("1")) {
System.out.println("Pythagoras Theorem");
System.out.print("Insert side a: ");
double a = scanner.nextDouble();
System.out.print("Insert side b: ");
double b = scanner.nextDouble();
double c = pitagoras(a, b);
System.out.println("Hypotenuse c: " c);
} else if (firstQuestion.equals("2")) {
System.out.println("Square area");
System.out.print("Insert side a: ");
double arestaA = scanner.nextDouble();
System.out.print("Insert side b: ");
double arestaB = scanner.nextDouble();
double squareArea = squarearea(arestaA, arestaB);
System.out.println("The square area is: " squareArea);
} else if (firstQuestion.equals("3")) {
// Triangle area
} else if (firstQuestion.equals("4")) {
exit = true;
} else {
printMenu = false;
System.out.println("Please insert a valid formula number.");
}
} while (!exit);
}
// methods parameters
static double pitagoras(double a, double b) {
double c = Math.sqrt((a * a) (b * b));
return c;
}
static double squarearea(double a, double b) {
double area = a * b;
return area;
}
}
CodePudding user response：
You can simply wrap your code starting from firstQuestion variable declaration till the end of the if condition in a while loop which is always set to true.
public class Formulas {
public static void main(String[] args) {
// first question
// constant values definition
final double PI = 3.141592653589793238;
// index
ArrayList<String> index = new ArrayList<>();
index.add("1. Pythagorean Theorem");
index.add("2. Square Area");
index.add("2. Triangle Area");
System.out.println("Formulas Index:");
System.out.println("");
for (int i = 0; i < index.size(); i ) {
System.out.println(index.get(i));
}
Scanner scanner = new Scanner(System.in);
while (true) {
System.out.println("");
System.out.print("Write the formulas number you want to use: ");
String firstQuestion = scanner.nextLine();
System.out.println();
// methods selection
if (firstQuestion.equals("1")) {
System.out.println("Pythagoras Theorem");
System.out.print("Insert side a: ");
double a = scanner.nextDouble();
System.out.print("Insert side b: ");
double b = scanner.nextDouble();
double c = pitagoras(a, b);
System.out.println("Hypotenuse c: " c);
} else if (firstQuestion.equals("2")) {
System.out.println("Square area");
System.out.print("Insert side a: ");
double arestaA = scanner.nextDouble();
System.out.print("Insert side b: ");
double arestaB = scanner.nextDouble();
double squareArea = squarearea(arestaA, arestaB);
System.out.println("The square area is: " squareArea);
} else
System.out.println("Please insert a valid formula number.");
}
}
// methods parameters
static double pitagoras(double a, double b) {
double c = Math.sqrt((a * a) (b * b));
return c;
}
static double squarearea(double a, double b) {
double area = a * b;
return area;
}
}