I am new to java and this is my first program, I'm very confused with these errors and have looked everywhere for the answer. please help!
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner myObj = new Scanner(System.in);
System.out.println("Enter first number");
String str1 = myObj.nextLine();
System.out.println("Enter Operator");
String op = myObj.nextLine();
System.out.println("Enter second number");
String str2 = myObj.nextLine();
int num1 = Integer.parseInt(str1);
int num2 = Integer.parseInt(str2);
if (op.equals("+")) {
int ans = (num1 + num2);
} else if (op.equals("-")){
int ans = (num1 - num2);
}
System.out.println(num1 + " " + op + " " + num2 + " = " + ans);
}
}
Then it gives me these errors, I'm using IntelliJ idea
Cannot resolve symbol 'ans'
Variable 'ans' is never used
Variable 'ans' is never used
Cannot resolve symbol 'ans'
Declare ans outside the if:
int ans = 0;
if (op.equals("+")) {
ans = (num1 + num2);
} else if (op.equals("-")){
ans = (num1 - num2);
}
System.out.println(num1 + " " + op + " " + num2 + " = " + ans);
otherwise it is never visible in the line where it is used in System.out.println
Variable 'ans' is never used
Variable 'ans' is never used
In your code ans is declared in the if - code blocks, and after assignment those ans are no longer used, because code-block in if ends just after the assignment.
Related
The result i get :
Enter a number :
5
Enter another number :
4
What do you want to perform on these numbers?
You have entered a wrong action, please try again
Where did i go wrong in my code?
import java.util.Scanner;
public class App {
public static void main(String[] args) {
double num1, num2;
Scanner sc = new Scanner(System.in);
System.out.println("Enter a number : ");
num1 = sc.nextDouble();
System.out.println("Enter another number : ");
num2 = sc.nextDouble();
System.out.println("What do you want to perform on these numbers? ");
String word = sc.nextLine();
sc.close();
double result = 0;
switch (word) {
case "Addition":
result = num1 + num2;
System.out.println(num1 + " " + word + " " + num2 + " : " + result);
break;
case "Subtraction":
result = num1 - num2;
System.out.println(num1 + " " + word + " " + num2 + " : " + result);
break;
case "Multiplication":
result = num1 * num2;
System.out.println(num1 + " " + word + " " + num2 + " : " + result);
break;
case "Division":
result = num1 / num2;
System.out.println(num1 + " " + word + " " + num2 + " : " + result);
break;
default:
System.out.println("You have entered a wrong action, please try again ");
break;
}
}
}
Instead of using sc.nextline() on line 15 use sc.next(). The program will now wait for your input before continuing.
Can you change your code like below:
System.out.println("What do you want to perform on these numbers? ");
sc.nextLine(); // ADD THIS LINE
String word = sc.nextLine();
The problem here is with the num2 = sc.nextDouble(); the newline char is not consumed.
Below is the code I use:
public static void main(String args[]) throws Exception {
// A1Pattern.printPattern(26);
double num1, num2;
Scanner sc = new Scanner(System.in);
System.out.println("Enter a number : ");
num1 = sc.nextDouble();
System.out.println("Enter another number : ");
num2 = sc.nextDouble();
System.out.println("What do you want to perform on these numbers? ");
sc.nextLine();
String word = sc.nextLine();
sc.close();
double result = 0;
switch (word) {
case "Addition":
result = num1 + num2;
System.out.println(num1 + " " + word + " " + num2 + " : " + result);
break;
case "Subtraction":
result = num1 - num2;
System.out.println(num1 + " " + word + " " + num2 + " : " + result);
break;
case "Multiplication":
result = num1 * num2;
System.out.println(num1 + " " + word + " " + num2 + " : " + result);
break;
case "Division":
result = num1 / num2;
System.out.println(num1 + " " + word + " " + num2 + " : " + result);
break;
default:
System.out.println("You have entered a wrong action, please try again ");
break;
}
}
OUTPUT:
Enter a number :
1
Enter another number :
2
What do you want to perform on these numbers?
Subtraction
1.0 Subtraction 2.0 : -1.0
The java.util.Scanner.next() method finds and returns the next complete token from this scanner.
Use scanner.next() instead of scanner.nextLine().
i'm beginner for java.
I have a project for final mark. I did something but i need your help.
My project is about mathematical operations. I should use JOptionPane.
I could first part InputDialog But I can't show them in the messagebox ( i used println only to see how to work). And of course the division part is very important. If you try to divide by zero it should be error and should write something about error. I'm waiting your help. Thanks a lot and best regards.
import javax.swing.JOptionPane;
public class JavaMath3 {
public static void main(String[] args) {
int num1, num2, add, sub, multi;
double div;
num1 = Integer.parseInt(JOptionPane.showInputDialog("Write 1st number."));
num2 = Integer.parseInt(JOptionPane.showInputDialog("Write 2nd number."));
add = num1+num2;
System.out.println("Addition " + add);
sub = num1-num2;
System.out.println("Subtraction " + sub);
multi = num1*num2;
System.out.println("Multiplication " + multi);
if(num2 != 0 ) {
div = (double) num1/num2;
System.out.println("Division: " + div);
}
else {
System.out.println("A number can not divided by zero.");
}
}
}
it's a very simple you can use the JOPtionPane method showMessageDialog
JOptionPane.showMessageDialog(parent, "your message");
and here's a sample code
public static void main(String[] args)
{
int num1 = Integer.parseInt(JOptionPane.showInputDialog("Write 1st number."));
int num2 = Integer.parseInt(JOptionPane.showInputDialog("Write 2nd number."));
int sum = num1 + num2;
JOptionPane.showMessageDialog(null, "sum = " + sum);
}
After update
here's a complete example
public static void main(String[] args)
{
int num1, num2, add, sub, multi;
double div;
num1 = Integer.parseInt(JOptionPane.showInputDialog("Write 1st number."));
num2 = Integer.parseInt(JOptionPane.showInputDialog("Write 2nd number."));
add = num1 + num2;
sub = num1 - num2;
multi = num1 * num2;
String result = "sum = " + add + "\n" + "sub = " + sub + "\nmul = " + multi;
if (num2 != 0)
{
div = (double) num1 / num2;
result = result + " \n div = " + div;
} else
{
result = result + " \n div = A number can not divided by zero";
System.out.println("A number can not divided by zero.");
}
JOptionPane.showMessageDialog(null, result);
}
I don't get what mean by box but if you want them all in a same dialog box you could just write this line after your else statement:
JOptionPane.showMessageDialog(null, "Addition: " + add+ "\nSubtraction: " + sub+"\nMultiplication " + multi+ "\nDivision: " + div);
I am attempting to simplify my long code of a calculator program, but I have a road block. I have a new else if statement for each calculator operator, but what I want to do is allow the user to manually type in, on one line, the entire operation they would like to perform and have the code compute it.
Here's what I have:
do {
System.out.println("What function would you like to perform?");
System.out.print("Exit Calculator (Q), Add (+), Subtract (-), Multiply (x), Divide (/): ");
maininput = in.next();
if (maininput.equals("+")) {
System.out.print("Enter the first number to add: ");
num1 = in.nextDouble();
System.out.print("Enter the second number to add: ");
num2 = in.nextDouble();
System.out.println();
answer = num1 + num2;
System.out.println(num1 + " + " + num2 + " = " + answer);
System.out.println();
}
else if (maininput.equals("-")) {
System.out.print("Enter the first number to subtract: ");
num1 = in.nextDouble();
System.out.print("Enter the second number to subtract: ");
num2 = in.nextDouble();
System.out.println();
answer = num1 - num2;
System.out.println(num1 + " - " + num2 + " = " + answer);
System.out.println();
}
else if(maininput.equals("x")) {
System.out.print("Enter the first number to multiply: ");
num1 = in.nextDouble();
System.out.print("Enter the second number to multiply: ");
num2 = in.nextDouble();
System.out.println();
answer = num1 * num2;
System.out.println(num1 + " x " + num2 + " = " + answer);
System.out.println();
}
else if(maininput.equals("/")) {
System.out.print("Enter the first number to divide: ");
num1 = in.nextDouble();
do {
System.out.print("Enter the second number to divide: ");
num2 = in.nextDouble();
System.out.println();
if (num2 == 0) {
System.out.println("Cannot divide by 0! Please enter a different number.");
}
} while (num2 == 0);
answer = num1 / num2;
System.out.println(num1 + " / " + num2 + " = " + answer);
System.out.println();
}
else if(maininput.equals("Q") || maininput.equals("q") || maininput.equals("EXIT") || maininput.equals("exit")) {
in.close();
System.exit(0);
}
else {
System.out.println(maininput + " is not a valid operand. Please try again.");
System.out.println();
}
} while (maininput != "Q" && maininput != "q");
This is what I want the output to be:
Enter operation:
4 * 6
4 * 6 = 24
Should be able to enter any operation here on one line. I am not asking you to write my calculator for me, I am asking how to allow the computer to read in the entire operation off one line and compute it, then print it.
If you use scanner readLine then you can read a whole line
e.g.
4 * 6
This line can then be split to get three tokens
String tokens [] = line.split (" ");
then you can see what operation to do based upon token[1]
if (token[1].equals ("-") {
//lets minus token[2] from token[0]
// need to convert String to Number
}
You can use String.split and store it in an array. Then it will return an array of string, parse those back to integers. the do the operation you want. The x variable will be the result.
if(maininput.contains("+")) {
String[] stringarr = string.split("\\+");
int x = Integer.parseInt(stringarr[0]) + Integer.parseInt(stringarr[1]);
System.out.println(stringarr[0] + " + " + stringarr[1] + " = " + x);
} else if(maininput.contains("-")) {
String[] stringarr = string.split("\\-");
int x = Integer.parseInt(stringarr[0]) - Integer.parseInt(stringarr[1]);
System.out.println(stringarr[0] + " - " + stringarr[1] + " = " x);
}
... And so on.
You could try parsing the line using a Pattern object, something like this:
Pattern opPattern = Pattern.compile("(\\d+) *([+-*/]) *(\\d+)");
Matcher matcher = opPattern.matcher(userLine);
if(matcher.find()) {
int op1 = Integer.toValue(matcher.group(1));
int op2 = Integer.toValue(matcher.group(3));
String op = matcher.group(2);
if(op.equals("+")) {
// do + op ...
} else ... {
// etc...
}
} else {
// error in line, not the form of an operation
}
Have a look at the javadoc, as I'm not sure if I used the correct method names and the like, just tried to illustrate the idea...
This program is designed to add 2 random numbers generated by the computer, when the user answer goes wrong , the computer tells the user to try it again, by using the while loop. The program will stop once the user enters a correct number. I have to calculate the wrong count in the while loop, however, it gives me the wrong count 1 when it is the second attempt.Please be kind enough to tell me where I go wrong in the code. Thank you.
import java.util.Scanner;
public class add {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int num1 = (int) (Math.random() * 10);
int num2 = (int) (Math.random() * 10);
int wrong = 0;
System.out.println("What is " + num1 + "+" + num2 + "=" + "?");
int answer = input.nextInt();
while (num1 + num2 != answer) {
System.out.println("Wrong answer, Try again . " +
"What is " + num1 + "+" + num2 + "? ");
answer = input.nextInt();
System.out.println("The number of attemt is " + wrong);
++wrong;
}
System.out.println("You got it correct !");
}
}
The error is in incrementing the number the user has gotten wrong AFTER printing "You got x wrong"
Just put ++wrong above System.out.println("The number of attemt is " + wrong);
while (num1 + num2 != answer) {
System.out.println("Wrong answer, Try again . " +
"What is " + num1 + "+" + num2 + "? ");
answer = input.nextInt();
++wrong;
System.out.println("The number of attemt is " + wrong);
}
Just change
wrong = 0
to
wrong = 1
wrong should probably be renamed to numberOfAttempts.
Initialize wrong to 1 instead of 0.
int wrong = 1;
A more appropriate name for the variable would be attempt if you take this approach.
You need to increment wrong before you display it:
import java.util.Scanner;
public class Add {
public static void main(String[] args ){
Scanner input = new Scanner (System.in);
int num1 = (int)(Math.random() * 10);
int num2 = (int)(Math.random() * 10);
int wrong = 0 ;
System.out.println("What is " + num1 + "+" + num2 + "=" + "?");
int answer = input.nextInt();
while (num1 + num2 != answer){
wrong++ ;
System.out.println("Wrong answer, Try again . What is " + num1 +"+"+ num2 + "? " );
answer = input.nextInt();
System.out.println("The number of attempt is " + wrong);
}
System.out.println("You got it correct !");
}
}
This question already has answers here:
Using scanner.nextLine() [duplicate]
(5 answers)
Scanner issue when using nextLine after nextXXX [duplicate]
Closed 9 years ago.
I'm relatively new to programming and have recently started learning Java in order to move into Android programming. I thought I would create a very simple calculator to practice, but it seems that my if statement doesn't work.
import java.util.Scanner;
public class Calculator {
public static void main(String[] args) {
//Create new scanner object
Scanner numInput = new Scanner( System.in );
//Enter first number
System.out.println("Please enter the first number: ");
int num1 = numInput.nextInt();
//Enter the second number
System.out.println("Please enter the second number: ");
int num2 = numInput.nextInt();
//Choose the operation to perform (+,-,*,/)
System.out.println("What operation would you like to do?");
System.out.println("Type \"+\" to add.");
System.out.println("Type \"-\" to subtract.");
System.out.println("Type \"*\" to multiply.");
System.out.println("Type \"/\" to divide.");
String opChoice = numInput.nextLine();
//Add
if (opChoice.equals("+")) {
int ans = num1 + num2;
System.out.println("Adding " + num2 + " to " + num1 + " equals " + ans + ".");
}
//Subtract
else if (opChoice.equals("-")) {
int ans = num1 - num2;
System.out.println("Subtracting " + num2 + " from " + num1 + " equals " + ans + ".");
}
//Multiply
else if (opChoice.equals("*")) {
int ans = num1 + num2;
System.out.println("Multiplying " + num2 + " with " + num1 + " equals " + ans + ".");
}
//Divide
else if (opChoice.equals("/")) {
int ans = num1 + num2;
System.out.println("Dividing " + num1 + " by " + num2 + " equals " + ans + ".");
}
}
}
I am using the Eclipse IDE, and it runs fine until it asks for which operation to do. It will display the options but won't let me enter anything (I've been testing it with multiplying 5 by 2).
I searched for similar questions and tried what they suggested, but it still doesn't seem to work. I would appreciate any help, I assume this is probably just some simple error I am making, so I apologize if this seems like a silly question!
EDIT: Thanks for the quick responses, guys! I appreciate it. And yes, I fixed the multiply and division. :)
The problem is that nextInt() doesn't consume (doesn't read) the new-line character (that you input when you press [Enter]). One way to solve this is calling nextLine() after each nextInt():
//Enter first number
System.out.println("Please enter the first number: ");
int num1 = numInput.nextInt();
numInput.nextLine(); // Add this
//Enter the second number
System.out.println("Please enter the second number: ");
int num2 = numInput.nextInt();
numInput.nextLine(); // Add this
Another way to solve this, would be reading the numbers with nextLine() (which returns a String) and then parsing it to a int:
int num1 = Integer.parseInt(numInput.nextLine());
You won't need to add an extra nextLine() because the new-line character is being consumed by the nextLine() already called.
Also, as #sotondolphin suggested, you may want to check your * and / operations.
The issue is that when numInput.nextInt(); is called, you get the number entered ... but it leaves the newline (\n). Your call to numInput.nextLine(); then gets an empty string.
Replacing that call with numInput.next() will solve the problem as it has a slightly different behavior:
public String next()
Finds and returns the next complete token from this scanner. A complete token is preceded and followed by input that matches the delimiter pattern.
The default delimiter pattern is whitespace, which includes \n and what's in the input stream after you enter the operation (using * as example) is now \n*\n
The code below does addition but not expected multiplication and division. Could you please check the source?
//Multiply
else if (opChoice.equals("*")) {
int ans = num1 + num2;
System.out.println("Multiplying " + num2 + " with " + num1 + " equals " + ans + ".");
}
//Divide
else if (opChoice.equals("/")) {
int ans = num1 + num2;
System.out.println("Dividing " + num1 + " by " + num2 + " equals " + ans + ".");
}
}